- Email: [email protected]
Pneumococcal serotype distribution among meningitis cases from Togo and Burkina Faso during 2007–2009
Vaccine 30S (2012) G41–G45
Contents lists available at SciVerse ScienceDirect
Vaccine journal homepage: www.elsevier.com/locate/vaccine
Review
Pneumococcal serotype distribution among meningitis cases from Togo and Burkina Faso during 2007–2009 Bradford D. Gessner a,∗ , Oumarou Sanou b , Aly Drabo c , Tsidi Agbeko Tamekloe d , Seydou Yaro c , Haoua Tall b , Jennifer C. Moïsi a , Judith E. Mueller a,1 , Berthe-Marie Njanpop-LaFourcade a a
Agence de Medecine Preventive, Paris, France Agence de Medecine Preventive at Centre Muraz, Bobo-Dioulasso, Burkina Faso c Centre Muraz, Bobo-Dioulasso, Burkina Faso d Ministere de la Sante Publique du Togo, Lome, Togo b
a r t i c l e
i n f o
Article history:
Keywords: Africa Burkina Faso Meningitis Pneumococcus Serotype Streptococcus pneumoniae Togo Vaccine
a b s t r a c t We evaluated pneumococcal serotype/group distribution using polymerase chain reaction (PCR) testing on cerebrospinal fluid collected from patients from Burkina Faso and Togo who presented for care during 2007–2009. We identified 282 pneumococcal meningitis cases based on PCR, latex agglutination, or culture, of which 206 underwent serotyping. Serotype 1 was identified for 18% of serotyped cases from patients aged <5 years and 66% of those aged ≥5 years. The 13-valent and 10-valent pneumococcal conjugate vaccines (PCV-13 and PCV-10) contain 53% of serotypes identified among children age <5 years and 76–77% among persons aged ≥5 years. Pneumococcal meningitis was highly seasonal regardless of serotype. Data from this study emphasize the potential usefulness of PCVs among older children and adults. © 2012 Elsevier Ltd. All rights reserved.
Contents 1. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction As we and others have reported previously, the African meningitis belt has a unique pneumococcal meningitis epidemiology with high incidence in all age groups, high case fatality ratios, and a predominance of serotype 1 after the first five years of life [1–4]. In a 9-valent pneumococcal conjugate vaccine (PCV) trial in The Gambia, on the border of the belt, receipt of vaccine was associated with a 77% reduction in vaccine-serotype invasive disease, a 7% decrease in clinical pneumonia and a decrease in infant mortality
∗ Corresponding author at: 164 Rue du Vaugirard, Paris, France. Tel.: +33 1 5386 8920; fax: +33 1 5386 8939. E-mail address: [email protected] (B.D. Gessner). 1 Agence de Medecine Preventive when contributing to this work; currently Ecole des Hautes Etudes en Sante Publique, Paris, France. 0264-410X/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.vaccine.2012.10.052
G41 G41 G42 G43 G44
of 5 per 1000 live births [5]. Achieving long-term impact on morbidity and mortality within the belt will depend on numerous factors including the magnitude and duration of immunity following immunization and natural exposure to pneumococcal antigen, age- and serotype-specific carriage dynamics, and variations in serotype-specific disease incidence over time. Both natural and vaccine-driven fluctuations in serotype-specific disease are expected [6]. To help inform this issue, we present an update on pneumococcal serotype distribution in Togo and Burkina Faso prior to PCV introduction into routine infant immunization programs. 2. Methods Data were available from both Burkina Faso and Togo for 2007–2009. Methods and populations were in general as previously
G42
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
described [4,7]. In brief, we included the regional referral hospital in Bobo-Dioulasso, Burkina Faso, which served four districts (Dafra, Do, K. Vigue, and Lena); we also included referral hospitals in the cities of Dapaong, Kara, Sokode, and Sotouboua representing four districts in Central and Northern Togo (Tone, Kozah, Tchaoudjo, and Sotouboua). Physicians identified suspected meningitis cases based on their clinical judgment and WHO guidelines, with symptoms generally including rapid onset of fever and at least one common sign of meningitis, regardless of age. All patients had a lumbar puncture. The reference laboratory in Bobo-Dioulasso performed all laboratory testing of patients from Burkina Faso. For patients from Togo, latex agglutination and culture were performed locally while polymerase chain reaction (PCR) was performed in Bobo-Dioulasso; cerebrospinal fluid (CSF) specimens were kept frozen until sent at ambient temperature. CSF was cultured using standard methodology [8]. Latex agglutination testing used Pastorex (Biorad) and was performed according to the manufacturer’s instructions. PCR identification of pneumococcus was based on amplification of the lytA gene [9]. If pneumococcus was identified by any of the testing methodologies, we performed pneumococcal serotyping of CSF using sequential multiplex polymerase chain reaction (PCR) testing in Bobo-Dioulasso [10–12]. The serotyping algorithm currently includes 40 serotypes/groups (1, 2, 3, 4, 5, 6A/6B/6C/6D, 6C/D, 7C/[7B/40], 7F/7A, 8, 9N/9L, 9V/9A, 10A, 10F/[10C/33C], 11A/11D, 12F/[12A/44/46], 13, 14, 15A/15F, 15B/15C, 16F, 17F, 18/[18A/18B/18C/18F], 19A, 19F, 20, 21, 22F/22A, 23A, 23B, 23F, 24/[24A,24B,24F], 31, 33F/[33A/37], 34, 35A/[35C/42], 35B, 35F/47F, 38/25F/25A, 39) (see website: http://www.cdc.gov/ncidod/biotech/strep/pcr.htm, accessed 03.09.12). If CSF was lytA positive but the serotyping algorithm yielded negative results, we considered the pneumococcal serotype to be indeterminate. In addition to PCR testing of CSF in Bobo-Dioulasso, we sent a sample of pneumococci to the German Reference Center for Streptococci in Aachen, where isolates were serotyped using Neufeld Quellung’s reaction [13]. This surveillance project was approved by the ethical review board of Centre Muraz in Burkina Faso and was supported by the Ministries of Health of Burkina Faso and Togo.
3. Results We identified 282 pneumococcal cases from CSF during 2007–2009, including 120 (43%) by culture, 130 (46%) by latex agglutination, and 249 (88%) by PCR; for 112 patients (40%), identification was by PCR alone. Of the 282 pneumococcal cases, 157 (56%) resided in Burkina Faso and the remainder in Togo. Within Burkina Faso, 129 cases (82%) were from Dafra and Do Districts while in Togo, 94 cases (75%) were from Kozah and Tone Districts. Males represented 158 (56%) of cases. There were 31 children (11%) aged <6 months, 16 (5.7%) aged 6–11 months, 25 (8.9%) 1–4 years, 93 (33%) 5–14 years, 96 (34%) 15–49 years, and 19 (6.7%) age 50 years or older. Of the 282 pneumococcal cases, serotyping was performed for 206 (73%). PCR was performed in Bobo-Dioulasso for 204 (two cases had Quellung performed on isolates but had insufficient CSF for PCR testing). For 19 cases, results were available from PCR and Quellung and in all cases there was agreement between the two methods. Quellung was not performed for any pneumococcal meningitis cases that could not be serotyped using our PCR algorithm. Results reported below use the more specific Quellung data where available, and otherwise data from PCR. Serotype 1 was identified in 106 cases (51%), while no other serotype contributed to more than 8% of the total; 34 cases (17%) could not be serotyped with our PCR algorithm (Fig. 1). Serotype 1, non-serotype 1, and PCV-13 serotypes all had the same seasonality, with peaks from January to March each year and little to no disease from July to December (Fig. 2). Serotype 1 predominated for all age groups with the notable exception of children <5 years of age (Table 1). Overall, serotypes contained in PCV-13 and PCV-10 constituted 53% of serotypes among children aged <5 years, a value that increased to 65% if all serogroup 18 cases were included. Among persons aged ≥5 years, PCV-13 and PCV-10 would provide coverage for 77% and 76% of identified serotypes, respectively (no serogroup 18 cases were identified in persons age ≥5 years). Serotypes contained in PCV-13 and PCV-10 other than serotype 1 constituted 11% and 10%, respectively, of total serotyped cases (including cases with indeterminate serotype) among persons aged ≥5 years and 35% of serotypes among children age <5 years (47% if all serogroup 18 cases
Fig. 1. Pneumococcal serotype/group distribution among meningitis cases from Burkina Faso and Togo tested primarily by polymerase chain reaction on cerebrospinal fluid; 2007–2009.
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
G43
Fig. 2. Distribution over time of pneumococcal meningitis cases from Burkina Faso and Togo, by serotype 1 status and whether the serotype is covered in the 13-valent pneumococcal conjugate vaccine; 2007–2009.
were included). The proportion of serotypes contained in PCV-13 and PCV-10 decreased from 2007 to 2008/9, primarily because of an increase in pneumococcal cases where our serotyping algorithm yielded negative results. 4. Discussion Based on one of the largest collections of serotypes yet reported from the African meningitis belt spanning a 3-year period before widespread use of PCV, we demonstrate the epidemiology of pneumococcal meningitis serotype distribution in Burkina Faso and Togo. Serotype 1 predominated in all age groups with the exception of children aged <5 years, and a strong seasonality was observed
regardless of serotype. These findings are consistent with earlier data from the meningitis belt and underscore the particularity of local disease patterns and the need for local evaluations of vaccine impact to support and sustain vaccine introduction. Our data point to four areas that require consideration: serotype coverage in children, vaccine effectiveness against serotype 1, use of PCVs outside of the pediatric population, and natural variations in serotype distribution even over relatively short time periods. First, we found that available PCVs would cover 50–65% of identified meningitis-causing serotypes among children aged <5 years, who are the primary target group for pneumococcal vaccination supported by the GAVI Alliance. Our data apply only to meningitis
Table 1 Characteristics of persons with acute bacterial meningitis who had pneumococcal serotype data; Burkina Faso and Togo, 2007–2009. Total pneumococcal cases serotyped
Serotype 1
PCV-10 serotypes
PCV-13 serotypes
PCV-13 serotypes + serogroup 18
Unknown serotypesa
Age group (in years) <5 <1 1 2 3 4 ≥5 5–9 10–14 15–19 20–24 25–29 30–34 35–39 40–44 45–49 50+
60 43 3 3 4 7 110 32 27 24 7 12 8 6 7 10 11
11 (18%) 5 (12%) 0 (0%) 1 (33%) 1 (25%) 4 (57%) 95 (66%) 22 (69%) 24 (89%) 17 (71%) 5 (71%) 6 (50%) 6 (75%) 3 (50%) 2 (29%) 5 (50%) 5 (45%)
32 (53%) 19 (44%) 3 (100%) 2 (67%) 2 (50%) 6 (86%) 110 (76%) 26 (81%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 4 (57%) 7 (70%) 6 (55%)
32 (53%) 19 (44%) 3 (100%) 2 (67%) 2 (50%) 6 (86%) 111 (77%) 26 (84%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 4 (57%) 7 (70%) 7 (64%)
39 (65%) 25 (58%) 3 (100%) 2 (67%) 3 (75%) 6 (86%) 111 (77%) 26 (81%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 5 (57%) 7 (70%) 7 (64%)
15 (25%) 13 (30%) 0 (0%) 0 (0%) 1 (25%) 1 (14%) 17 (12%) 2 (6%) 0 (0%) 1 (4%) 1 (14%) 2 (17%) 1 (13%) 3 (50%) 1 (14%) 3 (30%) 3 (27%)
Sex Male Female
115 87
57 (50%) 47 (54%)
79 (69%) 59 (68%)
80 (70%) 59 (68%)
84 (73%) 62 (71%)
23 (20%) 11 (13%)
Country Togo Burkina Faso
79 126
43 (54%) 63 (50%)
59 (75%) 83 (65%)
59 (75%) 84 (66%)
62 (78%) 88 (69%)
15 (19%) 19 (15%)
Year 2007 2008 2009
44 49 113
28 (64%) 21 (43%) 57 (50%)
39 (89%) 30 (61%) 73 (65%)
39 (89%) 31 (63%) 73 (65%)
40 (91%) 33 (67%) 77 (68%)
0 (0%) 5 (10%) 29 (26%)
Total
206
106 (51%)
142 (69%)
143 (69%)
150 (73%)
34 (17%)
a
In these cases, PCR testing was negative using our algorithm evaluating 40 serotypes/groups.
G44
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
and the implications for impact on pneumonia—the primary contributor to pneumococcal morbidity and mortality—remains unknown since serotype distribution for meningitis and pneumonia generally differ [14]. Pneumococci with indeterminate serotype on PCR likely represent serotypes not included in the PCR algorithm, which detects all serotypes in existing PCVs. Theoretically, a percentage of indeterminate serotype results may have occurred due to a limited sensitivity of conventional PCR to detect small quantities of DNA, which would have led us to underestimate the proportion of cases due to vaccine serotypes [10]. However, this seems unlikely since serotyping was only performed following identification of pneumococcus by PCR or the less sensitive methods of latex agglutination and culture. Additionally, our data are similar to an earlier paper we wrote for Burkina Faso and Togo that presented serotyping performed by a reference laboratory in France; in this paper 67% of 48 identified serotypes were included in PCV-13 and 39% in PCV-10 (or 67% if including cross-reactive serotype 6A). Second, the predominance of serotype 1 across the age spectrum emphasizes the need for a vaccine effective against this serotype. The only two efficacy trials of serotype 1-containing PCV showed conflicting and non-definitive results against serotype 1 disease [5,15]. Data from national surveillance in the United States [16], the United Kingdom (website: http://www. hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/Pneumococcal/ EpidemiologicalDataPneumococcal/CurrentEpidemiology Pneumococcal/InPrevenar13NotInPrevenarPCV7/pneumo07 Cummulativeweeklyunder2IN13NOTIN7vacc/, accessed 03.09.12) and Kenya (website: http://www.kemri-wellcome.org/pcviscurrent%20disease%20surveillance, accessed 03.09.12) show a decreasing incidence of serotype 1 invasive pneumococcal disease (IPD) after the introduction of PCV13 into routine immunization. These findings are promising but need to be buttressed by further data from Africa, if possible from the meningitis belt, to confirm the suitability of available PCVs in this population. Third, previous studies indicating a substantial meningitis burden among older children and adults [1–4,17]—in combination with our data demonstrating broad coverage of PCV-10 and PCV-13 against implicated serotypes—suggest that immunization outside of early childhood may be indicated. The US Food and Drug Administration has licensed PCV-13 for use in adults 50 years of age and above; licensure for persons aged 18–49 years is pending. While these populations may benefit indirectly from infant immunization [18], it is unknown whether these effects would materialize for serotype 1, as they are mediated through a reduction in nasopharyngeal colonization of vaccine-type pneumococci [19–21] and serotype 1 is rarely carried [22,23]. Comprehensive, population-based surveillance after introduction into routine infant immunization programs is required to monitor direct and indirect effects of vaccine and evaluate the potential benefits of vaccinating older age groups. Fourth, serotype distribution may change even in the absence of vaccine use. Previously, we reported that 14 of 18 (78%) serotypes among children aged <5 years were 1, 2, 5, and 6A [3,4]; by contrast, in the current study 45 of 60 (75%) serotypes/groups were 1, 14, 18, or indeterminate. While serotype stability was higher among older children and adults, this was due to the very high contribution of serotype 1 in all studies. During our earlier study, outside of serotype 1, there were 12 serotyped cases and nine identified serotypes; for the current study, 82% of the 47 nonserotype 1 pneumococci were serotype/group 6, 12F/12A/44/46, 14, 38/25F/25A, or indeterminate. During both studies, we documented variation in non-serotype 1 distribution even from one season to the next. The current paper presents one of the largest collections of pneumococcal serotypes from the meningitis belt and augments
data published previously from Burkina Faso and Togo. Data from the current paper are limited in that hospital- and health-center based surveillance may miss cases, particularly in very young children. Also, data on bacteremic pneumococcal pneumonia and other non-meningitis IPD syndromes are missing but essential for interpretation. Nevertheless, our findings highlight the importance of establishing long-term, comprehensive IPD surveillance before vaccine introduction to understand natural variations in pneumococcal serotype distribution and age patterns and to draw appropriate inferences from post-PCV introduction surveillance data. Conflict of interest: BD Gessner, O Sanou, H Tall, JC Moisi, JE Mueller, and BM Njanpop-LaFourcade all work for (or worked for in the case of Dr. Mueller) AMP, which receives unrestricted support from Sanofi-Pasteur and grant specific report from Crucell, GSK, Merck, Pfizer, and Sanofi-Pasteur. Pfizer and GSK are manufacturers of pneumococcal conjugate vaccines. References [1] Campagne G, Schuchat A, Djibo S, Ousséini A, Cissé L, Chippaux JP. Epidemiology of bacterial meningitis in Niamey, Niger, 1981–96. Bull World Health Organ 1999;77:499–507. [2] Leimkugel J, Adams Forgor A, Gagneux S, Pflüger V, Flierl C, Awine E, et al. An outbreak of serotype 1 Streptococcus pneumoniae meningitis in northern Ghana with features that are characteristic of Neisseria meningitidis meningitis epidemics. J Infect Dis 2005;192:192–9. [3] Yaro S, Lourd M, Traore Y, Njanpop-Lafourcade BM, Sawadogo A, Sangare L, et al. Epidemiological and molecular characteristics of a highly lethal pneumococcal meningitis epidemic in Burkina Faso. Clin Infect Dis 2006;43: 693–700. [4] Traore Y, Tameklo TA, Njanpop-Lafourcade BM, Lourd M, Yaro S, Niamba D, et al. Incidence, seasonality, age distribution, and mortality of pneumococcal meningitis in Burkina Faso and Togo. Clin Infect Dis 2009;48(Suppl 2): S181–9. [5] Cutts FT, Zaman SM, Enwere G, Jaffar S, Levine OS, Okoko JB, et al. Efficacy of nine-valent pneumococcal conjugate vaccine against pneumonia and invasive pneumococcal disease in The Gambia: randomised, double-blind, placebocontrolled trial. Lancet 2005;365:1139–46. [6] Weinberger DM, Malley R, Lipsitch M. Serotype replacement in disease after pneumococcal vaccination. Lancet 2011;378:1962–73. [7] Delrieu I, Yaro S, Tamekloe TA, Njanpop-Lafourcade BM, Tall H, Jaillard P, et al. Emergence of epidemic Neisseria meningitidis serogroup X meningitis in Togo and Burkina Faso. PLoS ONE 2011;6:e19513. [8] WHO. Laboratory methods for the diagnosis of meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae. WHO Communicable disease surveillance and response 1999 [WHO/CDS/CSR/EDC/99.7]. [9] Hassan-King M, Baldeh I, Adegbola R, Omosigho C, Usen SO, Oparaugo A, et al. Detection of Haemophilus influenzae and Streptococcus pneumoniae DNA in blood culture by a single PCR assay. J Clin Microbiol 1996;34:2030–2. [10] Njanpop Lafourcade BM, Sanou O, van der Linden M, Levina N, Karanfil M, Yaro S, et al. Serotyping pneumococcal meningitis cases in the African meningitis belt by use of multiplex PCR with cerebrospinal fluid. J Clin Microbiol 2010;48:612–4. [11] Dias CA, Teixeira LM, Carvalho MG, Beall B. Sequential multiplex PCR for determining capsular serotypes of pneumococci recovered from Brazilian children. J Med Microbiol 2007;56:1185–8. [12] Morais L, Carvalho MdaG, Roca A, Flannery B, Mandomando I, Soriano-Gabarró M, et al. Sequential multiplex PCR for identifying pneumococcal capsular serotypes from South-Saharan African clinical isolates. J Med Microbiol 2007;56:1181–4. [13] Neufeld F. Über die Agglutination der pneumokokken und über die theorie der agglutination. Z Hyg Infektionskr 1902;34:54–72. [14] Johnson HL, Deloria-Knoll M, Levine OS, Stoszek SK, Freimanis Hance L, Reithinger R, et al. Systematic evaluation of serotypes causing invasive pneumococcal disease among children under five: the pneumococcal global serotype project. PLoS Med 2010;7(10) [pii: e1000348]. [15] Klugman KP, Madhi SA, Huebner RE, Kohberger R, Mbelle N, Pierce N. A trial of a 9-valent pneumococcal conjugate vaccine in children with and those without HIV infection. N Engl J Med 2003;349:1341–8. [16] Moore M, Link-Gelles R, Farley M, Schaffner W, Thomas A, Reingold A, et al. Impact of 13-valent pneumococcal conjugate vaccine (PCV13) on invasive pneumococcal disease (IPD), US, 2010–11. In: 8th international symposium on pneumococci and pneumococcal diseases. 2012 [Abstract 179]. [17] Gessner BD, Mueller JE, Yaro S. African meningitis belt pneumococcal disease epidemiology indicates a need for an effective serotype 1 containing vaccine, including for older children and adults. BMC Infect Dis 2010; 10:22. [18] US Centers for Disease Control and Prevention. Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45 on incidence of invasive pneumococcal disease—United States, 1998–2003. Morb Mortal Wkly Rep 2005;54:893–7. [19] O’Brien KL, Millar EV, Zell ER, Bronsdon M, Weatherholtz R, Reid R, et al. Effect of pneumococcal conjugate vaccine on nasopharyngeal colonization among immunized and unimmunized children in a community-randomized trial. J Infect Dis 2007;196:1211–20. [20] Millar EV, O’Brien KL, Watt JP, Bronsdon MA, Dallas J, Whitney CG, et al. Effect of community-wide conjugate pneumococcal vaccine use in infancy on nasopharyngeal carriage through 3 years of age: a cross-sectional study in a high-risk population. Clin Infect Dis 2006;43:8–15. [21] Hammitt LL, Bruden DL, Butler JC, Baggett HC, Hurlburt DA, Reasonover A, et al. Indirect effect of conjugate vaccine on adult carriage of Streptococcus
G45
pneumoniae: an explanation of trends in invasive pneumococcal disease. J Infect Dis 2006;193:1487–94. [22] Roca A, Hill PC, Townend J, Egere U, Antonio M, Bojang A, et al. Effects of community-wide vaccination with PCV-7 on pneumococcal nasopharyngeal carriage in the Gambia: a cluster-randomized trial. PLoS Med 2011;8:e1001107. [23] Abdullahi O, Nyiro J, Lewa P, Slack M, Scott JA. The descriptive epidemiology of Streptococcus pneumoniae and Haemophilus influenzae nasopharyngeal carriage in children and adults in Kilifi district, Kenya. Pediatr Infect Dis J 2008;27:59–64.
Contents lists available at SciVerse ScienceDirect
Vaccine journal homepage: www.elsevier.com/locate/vaccine
Review
Pneumococcal serotype distribution among meningitis cases from Togo and Burkina Faso during 2007–2009 Bradford D. Gessner a,∗ , Oumarou Sanou b , Aly Drabo c , Tsidi Agbeko Tamekloe d , Seydou Yaro c , Haoua Tall b , Jennifer C. Moïsi a , Judith E. Mueller a,1 , Berthe-Marie Njanpop-LaFourcade a a
Agence de Medecine Preventive, Paris, France Agence de Medecine Preventive at Centre Muraz, Bobo-Dioulasso, Burkina Faso c Centre Muraz, Bobo-Dioulasso, Burkina Faso d Ministere de la Sante Publique du Togo, Lome, Togo b
a r t i c l e
i n f o
Article history:
Keywords: Africa Burkina Faso Meningitis Pneumococcus Serotype Streptococcus pneumoniae Togo Vaccine
a b s t r a c t We evaluated pneumococcal serotype/group distribution using polymerase chain reaction (PCR) testing on cerebrospinal fluid collected from patients from Burkina Faso and Togo who presented for care during 2007–2009. We identified 282 pneumococcal meningitis cases based on PCR, latex agglutination, or culture, of which 206 underwent serotyping. Serotype 1 was identified for 18% of serotyped cases from patients aged <5 years and 66% of those aged ≥5 years. The 13-valent and 10-valent pneumococcal conjugate vaccines (PCV-13 and PCV-10) contain 53% of serotypes identified among children age <5 years and 76–77% among persons aged ≥5 years. Pneumococcal meningitis was highly seasonal regardless of serotype. Data from this study emphasize the potential usefulness of PCVs among older children and adults. © 2012 Elsevier Ltd. All rights reserved.
Contents 1. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction As we and others have reported previously, the African meningitis belt has a unique pneumococcal meningitis epidemiology with high incidence in all age groups, high case fatality ratios, and a predominance of serotype 1 after the first five years of life [1–4]. In a 9-valent pneumococcal conjugate vaccine (PCV) trial in The Gambia, on the border of the belt, receipt of vaccine was associated with a 77% reduction in vaccine-serotype invasive disease, a 7% decrease in clinical pneumonia and a decrease in infant mortality
∗ Corresponding author at: 164 Rue du Vaugirard, Paris, France. Tel.: +33 1 5386 8920; fax: +33 1 5386 8939. E-mail address: [email protected] (B.D. Gessner). 1 Agence de Medecine Preventive when contributing to this work; currently Ecole des Hautes Etudes en Sante Publique, Paris, France. 0264-410X/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.vaccine.2012.10.052
G41 G41 G42 G43 G44
of 5 per 1000 live births [5]. Achieving long-term impact on morbidity and mortality within the belt will depend on numerous factors including the magnitude and duration of immunity following immunization and natural exposure to pneumococcal antigen, age- and serotype-specific carriage dynamics, and variations in serotype-specific disease incidence over time. Both natural and vaccine-driven fluctuations in serotype-specific disease are expected [6]. To help inform this issue, we present an update on pneumococcal serotype distribution in Togo and Burkina Faso prior to PCV introduction into routine infant immunization programs. 2. Methods Data were available from both Burkina Faso and Togo for 2007–2009. Methods and populations were in general as previously
G42
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
described [4,7]. In brief, we included the regional referral hospital in Bobo-Dioulasso, Burkina Faso, which served four districts (Dafra, Do, K. Vigue, and Lena); we also included referral hospitals in the cities of Dapaong, Kara, Sokode, and Sotouboua representing four districts in Central and Northern Togo (Tone, Kozah, Tchaoudjo, and Sotouboua). Physicians identified suspected meningitis cases based on their clinical judgment and WHO guidelines, with symptoms generally including rapid onset of fever and at least one common sign of meningitis, regardless of age. All patients had a lumbar puncture. The reference laboratory in Bobo-Dioulasso performed all laboratory testing of patients from Burkina Faso. For patients from Togo, latex agglutination and culture were performed locally while polymerase chain reaction (PCR) was performed in Bobo-Dioulasso; cerebrospinal fluid (CSF) specimens were kept frozen until sent at ambient temperature. CSF was cultured using standard methodology [8]. Latex agglutination testing used Pastorex (Biorad) and was performed according to the manufacturer’s instructions. PCR identification of pneumococcus was based on amplification of the lytA gene [9]. If pneumococcus was identified by any of the testing methodologies, we performed pneumococcal serotyping of CSF using sequential multiplex polymerase chain reaction (PCR) testing in Bobo-Dioulasso [10–12]. The serotyping algorithm currently includes 40 serotypes/groups (1, 2, 3, 4, 5, 6A/6B/6C/6D, 6C/D, 7C/[7B/40], 7F/7A, 8, 9N/9L, 9V/9A, 10A, 10F/[10C/33C], 11A/11D, 12F/[12A/44/46], 13, 14, 15A/15F, 15B/15C, 16F, 17F, 18/[18A/18B/18C/18F], 19A, 19F, 20, 21, 22F/22A, 23A, 23B, 23F, 24/[24A,24B,24F], 31, 33F/[33A/37], 34, 35A/[35C/42], 35B, 35F/47F, 38/25F/25A, 39) (see website: http://www.cdc.gov/ncidod/biotech/strep/pcr.htm, accessed 03.09.12). If CSF was lytA positive but the serotyping algorithm yielded negative results, we considered the pneumococcal serotype to be indeterminate. In addition to PCR testing of CSF in Bobo-Dioulasso, we sent a sample of pneumococci to the German Reference Center for Streptococci in Aachen, where isolates were serotyped using Neufeld Quellung’s reaction [13]. This surveillance project was approved by the ethical review board of Centre Muraz in Burkina Faso and was supported by the Ministries of Health of Burkina Faso and Togo.
3. Results We identified 282 pneumococcal cases from CSF during 2007–2009, including 120 (43%) by culture, 130 (46%) by latex agglutination, and 249 (88%) by PCR; for 112 patients (40%), identification was by PCR alone. Of the 282 pneumococcal cases, 157 (56%) resided in Burkina Faso and the remainder in Togo. Within Burkina Faso, 129 cases (82%) were from Dafra and Do Districts while in Togo, 94 cases (75%) were from Kozah and Tone Districts. Males represented 158 (56%) of cases. There were 31 children (11%) aged <6 months, 16 (5.7%) aged 6–11 months, 25 (8.9%) 1–4 years, 93 (33%) 5–14 years, 96 (34%) 15–49 years, and 19 (6.7%) age 50 years or older. Of the 282 pneumococcal cases, serotyping was performed for 206 (73%). PCR was performed in Bobo-Dioulasso for 204 (two cases had Quellung performed on isolates but had insufficient CSF for PCR testing). For 19 cases, results were available from PCR and Quellung and in all cases there was agreement between the two methods. Quellung was not performed for any pneumococcal meningitis cases that could not be serotyped using our PCR algorithm. Results reported below use the more specific Quellung data where available, and otherwise data from PCR. Serotype 1 was identified in 106 cases (51%), while no other serotype contributed to more than 8% of the total; 34 cases (17%) could not be serotyped with our PCR algorithm (Fig. 1). Serotype 1, non-serotype 1, and PCV-13 serotypes all had the same seasonality, with peaks from January to March each year and little to no disease from July to December (Fig. 2). Serotype 1 predominated for all age groups with the notable exception of children <5 years of age (Table 1). Overall, serotypes contained in PCV-13 and PCV-10 constituted 53% of serotypes among children aged <5 years, a value that increased to 65% if all serogroup 18 cases were included. Among persons aged ≥5 years, PCV-13 and PCV-10 would provide coverage for 77% and 76% of identified serotypes, respectively (no serogroup 18 cases were identified in persons age ≥5 years). Serotypes contained in PCV-13 and PCV-10 other than serotype 1 constituted 11% and 10%, respectively, of total serotyped cases (including cases with indeterminate serotype) among persons aged ≥5 years and 35% of serotypes among children age <5 years (47% if all serogroup 18 cases
Fig. 1. Pneumococcal serotype/group distribution among meningitis cases from Burkina Faso and Togo tested primarily by polymerase chain reaction on cerebrospinal fluid; 2007–2009.
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
G43
Fig. 2. Distribution over time of pneumococcal meningitis cases from Burkina Faso and Togo, by serotype 1 status and whether the serotype is covered in the 13-valent pneumococcal conjugate vaccine; 2007–2009.
were included). The proportion of serotypes contained in PCV-13 and PCV-10 decreased from 2007 to 2008/9, primarily because of an increase in pneumococcal cases where our serotyping algorithm yielded negative results. 4. Discussion Based on one of the largest collections of serotypes yet reported from the African meningitis belt spanning a 3-year period before widespread use of PCV, we demonstrate the epidemiology of pneumococcal meningitis serotype distribution in Burkina Faso and Togo. Serotype 1 predominated in all age groups with the exception of children aged <5 years, and a strong seasonality was observed
regardless of serotype. These findings are consistent with earlier data from the meningitis belt and underscore the particularity of local disease patterns and the need for local evaluations of vaccine impact to support and sustain vaccine introduction. Our data point to four areas that require consideration: serotype coverage in children, vaccine effectiveness against serotype 1, use of PCVs outside of the pediatric population, and natural variations in serotype distribution even over relatively short time periods. First, we found that available PCVs would cover 50–65% of identified meningitis-causing serotypes among children aged <5 years, who are the primary target group for pneumococcal vaccination supported by the GAVI Alliance. Our data apply only to meningitis
Table 1 Characteristics of persons with acute bacterial meningitis who had pneumococcal serotype data; Burkina Faso and Togo, 2007–2009. Total pneumococcal cases serotyped
Serotype 1
PCV-10 serotypes
PCV-13 serotypes
PCV-13 serotypes + serogroup 18
Unknown serotypesa
Age group (in years) <5 <1 1 2 3 4 ≥5 5–9 10–14 15–19 20–24 25–29 30–34 35–39 40–44 45–49 50+
60 43 3 3 4 7 110 32 27 24 7 12 8 6 7 10 11
11 (18%) 5 (12%) 0 (0%) 1 (33%) 1 (25%) 4 (57%) 95 (66%) 22 (69%) 24 (89%) 17 (71%) 5 (71%) 6 (50%) 6 (75%) 3 (50%) 2 (29%) 5 (50%) 5 (45%)
32 (53%) 19 (44%) 3 (100%) 2 (67%) 2 (50%) 6 (86%) 110 (76%) 26 (81%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 4 (57%) 7 (70%) 6 (55%)
32 (53%) 19 (44%) 3 (100%) 2 (67%) 2 (50%) 6 (86%) 111 (77%) 26 (84%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 4 (57%) 7 (70%) 7 (64%)
39 (65%) 25 (58%) 3 (100%) 2 (67%) 3 (75%) 6 (86%) 111 (77%) 26 (81%) 24 (89%) 18 (75%) 6 (86%) 9 (75%) 7 (88%) 3 (50%) 5 (57%) 7 (70%) 7 (64%)
15 (25%) 13 (30%) 0 (0%) 0 (0%) 1 (25%) 1 (14%) 17 (12%) 2 (6%) 0 (0%) 1 (4%) 1 (14%) 2 (17%) 1 (13%) 3 (50%) 1 (14%) 3 (30%) 3 (27%)
Sex Male Female
115 87
57 (50%) 47 (54%)
79 (69%) 59 (68%)
80 (70%) 59 (68%)
84 (73%) 62 (71%)
23 (20%) 11 (13%)
Country Togo Burkina Faso
79 126
43 (54%) 63 (50%)
59 (75%) 83 (65%)
59 (75%) 84 (66%)
62 (78%) 88 (69%)
15 (19%) 19 (15%)
Year 2007 2008 2009
44 49 113
28 (64%) 21 (43%) 57 (50%)
39 (89%) 30 (61%) 73 (65%)
39 (89%) 31 (63%) 73 (65%)
40 (91%) 33 (67%) 77 (68%)
0 (0%) 5 (10%) 29 (26%)
Total
206
106 (51%)
142 (69%)
143 (69%)
150 (73%)
34 (17%)
a
In these cases, PCR testing was negative using our algorithm evaluating 40 serotypes/groups.
G44
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45
and the implications for impact on pneumonia—the primary contributor to pneumococcal morbidity and mortality—remains unknown since serotype distribution for meningitis and pneumonia generally differ [14]. Pneumococci with indeterminate serotype on PCR likely represent serotypes not included in the PCR algorithm, which detects all serotypes in existing PCVs. Theoretically, a percentage of indeterminate serotype results may have occurred due to a limited sensitivity of conventional PCR to detect small quantities of DNA, which would have led us to underestimate the proportion of cases due to vaccine serotypes [10]. However, this seems unlikely since serotyping was only performed following identification of pneumococcus by PCR or the less sensitive methods of latex agglutination and culture. Additionally, our data are similar to an earlier paper we wrote for Burkina Faso and Togo that presented serotyping performed by a reference laboratory in France; in this paper 67% of 48 identified serotypes were included in PCV-13 and 39% in PCV-10 (or 67% if including cross-reactive serotype 6A). Second, the predominance of serotype 1 across the age spectrum emphasizes the need for a vaccine effective against this serotype. The only two efficacy trials of serotype 1-containing PCV showed conflicting and non-definitive results against serotype 1 disease [5,15]. Data from national surveillance in the United States [16], the United Kingdom (website: http://www. hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/Pneumococcal/ EpidemiologicalDataPneumococcal/CurrentEpidemiology Pneumococcal/InPrevenar13NotInPrevenarPCV7/pneumo07 Cummulativeweeklyunder2IN13NOTIN7vacc/, accessed 03.09.12) and Kenya (website: http://www.kemri-wellcome.org/pcviscurrent%20disease%20surveillance, accessed 03.09.12) show a decreasing incidence of serotype 1 invasive pneumococcal disease (IPD) after the introduction of PCV13 into routine immunization. These findings are promising but need to be buttressed by further data from Africa, if possible from the meningitis belt, to confirm the suitability of available PCVs in this population. Third, previous studies indicating a substantial meningitis burden among older children and adults [1–4,17]—in combination with our data demonstrating broad coverage of PCV-10 and PCV-13 against implicated serotypes—suggest that immunization outside of early childhood may be indicated. The US Food and Drug Administration has licensed PCV-13 for use in adults 50 years of age and above; licensure for persons aged 18–49 years is pending. While these populations may benefit indirectly from infant immunization [18], it is unknown whether these effects would materialize for serotype 1, as they are mediated through a reduction in nasopharyngeal colonization of vaccine-type pneumococci [19–21] and serotype 1 is rarely carried [22,23]. Comprehensive, population-based surveillance after introduction into routine infant immunization programs is required to monitor direct and indirect effects of vaccine and evaluate the potential benefits of vaccinating older age groups. Fourth, serotype distribution may change even in the absence of vaccine use. Previously, we reported that 14 of 18 (78%) serotypes among children aged <5 years were 1, 2, 5, and 6A [3,4]; by contrast, in the current study 45 of 60 (75%) serotypes/groups were 1, 14, 18, or indeterminate. While serotype stability was higher among older children and adults, this was due to the very high contribution of serotype 1 in all studies. During our earlier study, outside of serotype 1, there were 12 serotyped cases and nine identified serotypes; for the current study, 82% of the 47 nonserotype 1 pneumococci were serotype/group 6, 12F/12A/44/46, 14, 38/25F/25A, or indeterminate. During both studies, we documented variation in non-serotype 1 distribution even from one season to the next. The current paper presents one of the largest collections of pneumococcal serotypes from the meningitis belt and augments
data published previously from Burkina Faso and Togo. Data from the current paper are limited in that hospital- and health-center based surveillance may miss cases, particularly in very young children. Also, data on bacteremic pneumococcal pneumonia and other non-meningitis IPD syndromes are missing but essential for interpretation. Nevertheless, our findings highlight the importance of establishing long-term, comprehensive IPD surveillance before vaccine introduction to understand natural variations in pneumococcal serotype distribution and age patterns and to draw appropriate inferences from post-PCV introduction surveillance data. Conflict of interest: BD Gessner, O Sanou, H Tall, JC Moisi, JE Mueller, and BM Njanpop-LaFourcade all work for (or worked for in the case of Dr. Mueller) AMP, which receives unrestricted support from Sanofi-Pasteur and grant specific report from Crucell, GSK, Merck, Pfizer, and Sanofi-Pasteur. Pfizer and GSK are manufacturers of pneumococcal conjugate vaccines. References [1] Campagne G, Schuchat A, Djibo S, Ousséini A, Cissé L, Chippaux JP. Epidemiology of bacterial meningitis in Niamey, Niger, 1981–96. Bull World Health Organ 1999;77:499–507. [2] Leimkugel J, Adams Forgor A, Gagneux S, Pflüger V, Flierl C, Awine E, et al. An outbreak of serotype 1 Streptococcus pneumoniae meningitis in northern Ghana with features that are characteristic of Neisseria meningitidis meningitis epidemics. J Infect Dis 2005;192:192–9. [3] Yaro S, Lourd M, Traore Y, Njanpop-Lafourcade BM, Sawadogo A, Sangare L, et al. Epidemiological and molecular characteristics of a highly lethal pneumococcal meningitis epidemic in Burkina Faso. Clin Infect Dis 2006;43: 693–700. [4] Traore Y, Tameklo TA, Njanpop-Lafourcade BM, Lourd M, Yaro S, Niamba D, et al. Incidence, seasonality, age distribution, and mortality of pneumococcal meningitis in Burkina Faso and Togo. Clin Infect Dis 2009;48(Suppl 2): S181–9. [5] Cutts FT, Zaman SM, Enwere G, Jaffar S, Levine OS, Okoko JB, et al. Efficacy of nine-valent pneumococcal conjugate vaccine against pneumonia and invasive pneumococcal disease in The Gambia: randomised, double-blind, placebocontrolled trial. Lancet 2005;365:1139–46. [6] Weinberger DM, Malley R, Lipsitch M. Serotype replacement in disease after pneumococcal vaccination. Lancet 2011;378:1962–73. [7] Delrieu I, Yaro S, Tamekloe TA, Njanpop-Lafourcade BM, Tall H, Jaillard P, et al. Emergence of epidemic Neisseria meningitidis serogroup X meningitis in Togo and Burkina Faso. PLoS ONE 2011;6:e19513. [8] WHO. Laboratory methods for the diagnosis of meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae. WHO Communicable disease surveillance and response 1999 [WHO/CDS/CSR/EDC/99.7]. [9] Hassan-King M, Baldeh I, Adegbola R, Omosigho C, Usen SO, Oparaugo A, et al. Detection of Haemophilus influenzae and Streptococcus pneumoniae DNA in blood culture by a single PCR assay. J Clin Microbiol 1996;34:2030–2. [10] Njanpop Lafourcade BM, Sanou O, van der Linden M, Levina N, Karanfil M, Yaro S, et al. Serotyping pneumococcal meningitis cases in the African meningitis belt by use of multiplex PCR with cerebrospinal fluid. J Clin Microbiol 2010;48:612–4. [11] Dias CA, Teixeira LM, Carvalho MG, Beall B. Sequential multiplex PCR for determining capsular serotypes of pneumococci recovered from Brazilian children. J Med Microbiol 2007;56:1185–8. [12] Morais L, Carvalho MdaG, Roca A, Flannery B, Mandomando I, Soriano-Gabarró M, et al. Sequential multiplex PCR for identifying pneumococcal capsular serotypes from South-Saharan African clinical isolates. J Med Microbiol 2007;56:1181–4. [13] Neufeld F. Über die Agglutination der pneumokokken und über die theorie der agglutination. Z Hyg Infektionskr 1902;34:54–72. [14] Johnson HL, Deloria-Knoll M, Levine OS, Stoszek SK, Freimanis Hance L, Reithinger R, et al. Systematic evaluation of serotypes causing invasive pneumococcal disease among children under five: the pneumococcal global serotype project. PLoS Med 2010;7(10) [pii: e1000348]. [15] Klugman KP, Madhi SA, Huebner RE, Kohberger R, Mbelle N, Pierce N. A trial of a 9-valent pneumococcal conjugate vaccine in children with and those without HIV infection. N Engl J Med 2003;349:1341–8. [16] Moore M, Link-Gelles R, Farley M, Schaffner W, Thomas A, Reingold A, et al. Impact of 13-valent pneumococcal conjugate vaccine (PCV13) on invasive pneumococcal disease (IPD), US, 2010–11. In: 8th international symposium on pneumococci and pneumococcal diseases. 2012 [Abstract 179]. [17] Gessner BD, Mueller JE, Yaro S. African meningitis belt pneumococcal disease epidemiology indicates a need for an effective serotype 1 containing vaccine, including for older children and adults. BMC Infect Dis 2010; 10:22. [18] US Centers for Disease Control and Prevention. Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine
B.D. Gessner et al. / Vaccine 30S (2012) G41–G45 on incidence of invasive pneumococcal disease—United States, 1998–2003. Morb Mortal Wkly Rep 2005;54:893–7. [19] O’Brien KL, Millar EV, Zell ER, Bronsdon M, Weatherholtz R, Reid R, et al. Effect of pneumococcal conjugate vaccine on nasopharyngeal colonization among immunized and unimmunized children in a community-randomized trial. J Infect Dis 2007;196:1211–20. [20] Millar EV, O’Brien KL, Watt JP, Bronsdon MA, Dallas J, Whitney CG, et al. Effect of community-wide conjugate pneumococcal vaccine use in infancy on nasopharyngeal carriage through 3 years of age: a cross-sectional study in a high-risk population. Clin Infect Dis 2006;43:8–15. [21] Hammitt LL, Bruden DL, Butler JC, Baggett HC, Hurlburt DA, Reasonover A, et al. Indirect effect of conjugate vaccine on adult carriage of Streptococcus
G45
pneumoniae: an explanation of trends in invasive pneumococcal disease. J Infect Dis 2006;193:1487–94. [22] Roca A, Hill PC, Townend J, Egere U, Antonio M, Bojang A, et al. Effects of community-wide vaccination with PCV-7 on pneumococcal nasopharyngeal carriage in the Gambia: a cluster-randomized trial. PLoS Med 2011;8:e1001107. [23] Abdullahi O, Nyiro J, Lewa P, Slack M, Scott JA. The descriptive epidemiology of Streptococcus pneumoniae and Haemophilus influenzae nasopharyngeal carriage in children and adults in Kilifi district, Kenya. Pediatr Infect Dis J 2008;27:59–64.