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Varicella seroprevalence in a random sample of the Turkish population
Vaccine 20 (2002) 1425–1428
Varicella seroprevalence in a random sample of the Turkish population G. Kanra a,∗ , S. Tezcan b , S. Badur c , Turkish National Study Team1 a
Pediatric Infectious Disease Unit, Department of Pediatrics, Faculty of Medicine, Hacettepe University, 06100 Ankara, Turkey b Department of Public Health, Faculty of Medicine, Hacettepe University, Ankara, Turkey c Department of Microbiology, Faculty of Medicine, Istanbul University, Istanbul, Turkey Received 9 January 2001; received in revised form 20 September 2001; accepted 29 October 2001
Abstract Chicken pox highly contagious and common throughout the world, is an infectious disease caused by varicella zoster virus (VZV). This study was conducted to determine the seroprevalence of VZV in a population under age 30 and to identify the relationship of VZV seroprevalence and several characteristics of the study subjects in nine provinces of Turkey. The sampling method of 30 clusters recommended for field studies was used for selecting subjects of a pre-determined number in the rural and urban areas in each province. For this, a total of 60 groups, 30 clusters in the rural and 30 in the urban areas were determined. It was planned that a total of 4800 subjects, including 600 subjects from five big provinces (Istanbul, Ankara, Izmir, Adana, Diyarbakir) and 450 subjects from the remaining smaller provinces (Samsun, Erzurum, Trabzon, Edirne), be included in the study. ELISA method was used to examine the blood samples for VZV seropositivity. Positive VZV seroprevalence was detected in 77.8% of 4387 subjects under age 30 in nine provinces of Turkey. There was no difference in seroprevalence rate between rural and urban areas. Seroprevalence was found to be 79.0% in urban areas and 76.3% in rural areas. Seroprevalence increased with age. Seroprevalence was 20% at the age of 1 year, subsequently increased to 40% at the age of 4 years, 60% at the age 6 years, 80% at the age of 8 years, 85% at the age of 10 years, and then remained at 85–90% in subjects over the age of 10 years. In order to develop vaccination protocols and take appropriate preventive health care measures against diseases in different countries, it is very important to know the seroprevalence of any disease for an individual country. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: Varicella; Seroprevalance; Vaccine
1. Introduction Chicken pox is an infectious disease caused by varicella zoster virus (VZV). Ninety percent of all cases in the USA occur in children under the age of 15 years. The incidence of disease is similar in both sexes and different races. Virus from an infected person contaminates a healthy individual
via contact with fluids from skin lesions or droplets through respiratory system [1,2]. In general, life-long immunity develops following infection to chicken pox. This immunity depends on the antibody production as a result of cellular immunologic response. Cellular immunity may weaken with advancing age and the virus may be reactivated. Consequently, this reactivation
∗ Corresponding
author. Tel.: +90-312-3114963; fax: +90-312-3108241. H: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Atatürk University, Erzurum, Turkey. Bulut A: Professor of Public Health, Department of Pediatrics, Faculty of Medicine, Istanbul University, Istanbul, Turkey. Cin S: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ankara University, Ankara, Turkey. Çan G: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Karadeniz Technical University, Trabzon, Turkey. Dündar C: Pediatrician, Department of Pediatrics, Faculty of Medicine, 19 Mayis University, Samsun, Turkey. Egemen A: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ege University, Izmir, Turkey. Eskiocak M: Pediatrician, Department of Pediatrics, Faculty of Medicine, Trakya University, Ankara, Turkey. Evliyaoglu N: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Çukurova University, Adana Turkey. Güraksin A: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Atatürk University, Erzurum, Turkey. Mocan H: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Karadeniz Technical University, Trabzon, Turkey. Öztürk F: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, 19 Mayis University, Samsun, Turkey. Saka G: Pediatrician, Department of Pediatrics, Faculty of Medicine, Dicle University, Diyarbakir, Turkey. Sidal M: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Istanbul University, Istanbul, Turkey. Ulukol B: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ankara University, Ankara, Turkey. Tanyer G: Professor of Pediatrics, Ankara Hospital, Ministry of Health, Ankara, Turkey. Tas MA: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Dicle University, Diyarbakir, Turkey. Yazicioglu M: Pediatrician, Department of Pediatrics, Faculty of Medicine, Trakya University, Edirne, Turkey. Dagbasi N: Glaxo-SmithKline Beecham, Istanbul, Turkey. Velicangil Ö: Glaxo-SmithKline Beecham, Istanbul, Turkey. 1 Alp
0264-410X/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 0 1 ) 0 0 4 5 9 - 5
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G. Kanra et al. / Vaccine 20 (2002) 1425–1428
leads to pain and vesicles on the dermatome of sensory nerves, presenting as herpes zoster infection. [1,2]. Chicken pox is not a notifiable disease in Turkey. Moreover, because Turkey has not conducted a community-based study on this disease, the exact incidence is not known. Therefore, we conducted a study to determine the seroprevalence of VZV in the population under age 30 and to identify the relationship between VZV seroprevalence and several characteristics of the study subjects in nine provinces of Turkey. The subjects and locations provide a representative sample of geographic, demographic and socio-economical characteristics of Turkey.
2. Materials and methods The present study of seroprevalence of VZV was conducted in nine provinces of Turkey. The sampling method of 30 clusters was used for selecting subjects of a pre-determined number in the rural and urban areas in each province. This is a practical method recommended by World Health Organisation for field studies [3–5]. For this, a total of 60 clusters in the rural (30 clusters) and urban (30 cluster) areas were determined and the related lists were sent to the principal investigator in each city. The provinces included were Istanbul, Ankara, Izmir, Adana, Diyarbakir, Samsun, Trabzon, Erzurum and Edirne. Because one-third of Turkish population live in these areas, we believe that the seroprevalence of study subjects would be highly representative of the entire country. In addition to providing a representative cross sample, these provinces also draw intense migration from neighbouring cities and communities farther away. In each province, sample sizes were determined from published data on varicella seroprevalance and sample size formula for cluster sample size for each group of subjects under age 30 for seroprevalence estimates within 95% confidence rate [6]. Therefore, it was planned that a total of 4800 subjects, including 600 subjects from five big provinces (Istanbul, Ankara, Izmir, Adana, Diyarbakir) and 450 subjects from the remaining smaller provinces (Samsun, Erzurum, Trabzon, Edirne), be included in the study. These number were distributed among 0–30 years of age population of each province proportional to the actual size. The age groups were separated in to 5-year groups. The number and distribution of population in each province was obtained from the State Institute of Statistics. When the investigators reached the cluster (villages in rural area and streets in urban area) the door number to start was chosen randomly. Then until the predetermined number in each age group is reached houses were visited. In order to provide a standard practice, investigators in each centre were appropriately trained on such issues as the selecting subjects, obtaining informed consent, applying the questionnaire, taking blood sample, and collecting, storing
and transporting sera for the serum. Additionally, the authorised ethics committee in each centre approved this seroprevalence study, and the entire study was pre-approved by the ethics committee of the Ministry of Health. Each potential subject who was interviewed and who agreed to participate read and signed a written informed consent form. A questionnaire about several characteristics of subjects was used to obtain data on VZV epidemiology (for their parents or guardians supplied those under age 18, information). Following the interviews, appropriate blood samples were taken from subjects for seroprevalence analyses. Serum analyses were performed at the Microbiology Laboratory of Istanbul University Faculty of Medicine. Serum samples were obtained from the blood samples and transported to the related laboratory in accordance with the principles of cold chain. For each serum sample, a quantitative investigation for anti-varicella virus-IgG (anti-VZV-IgG) antibodies was performed using Dade-Behring micro-ELISA kits (Dade Behring Marburgh, Germany). The sensitivity and specificity of the ELISA method is approved especially for the field studies [7,8]. All serum samples including controls and references were diluted by 1/10 and added to two separate cupules, one containing viral antigen and the other containing control antigen. Following an incubation period of 60 min at 37 ◦ C, cupules were irrigated three times so that the unbounded materials were removed, then peroxidase-labelled anti-human conjugate (100 l) was added to the cupules. Following incubation period of of 60 min at 37 ◦ C cupules were irrigated again, and the chromogen substrate was added to the cupules. The reaction occurring in ELISA plates stored at room temperature for 30 min was terminated by adding 100 l of stopper buffer solution to each cupule. Subsequently, absorbency value for each cupule was detected by reading at 450 nm. By considering the absorbency values for cupules covered with or without antigen and using ␣-method, anti-VZV-IgG level was quantitatively determined for each serum sample. As this was a descriptive study only percentages were calculated and no further statistical analysis was made.
3. Results This seroprevalence study included a total of 4461 subjects representative of the population under age 30 in nine provinces of Turkey (Table 1). In Ankara, Izmir and Erzurum, more subjects than targeted sample size were questioned and subjected to blood analysis. The size of participation was also larger than expected, representing the population in related provinces. Generally, seroprevalences could not be determined in 5.1% of sampled subjects and 6.7% of interviewed subjects. The main reason for this was that blood sampling could not be performed in children under 1 year of age due to the difficulty of obtaining blood sample.
G. Kanra et al. / Vaccine 20 (2002) 1425–1428
1427
Table 1 Distribution of subjects selected for sampling, interviewed and underwent blood sampling in nine provinces (Turkey 1998) Provinces
Istanbul Ankara Izmir Adana Diyarbakir Samsun Erzurum Trabzon Edirne Total a b
Number of sampled subjects
600 600 600 600 600 450 450 450 450 4800
Positive seroprevalence
Number of interviewed subjects
79.8 78.2 73.2 80.9 83.6 75.8 76.9 78.2 69.7 77.8
Number of subjects undergoing blood analysis
Number
Percentagea
Number
Percentageb
563 636 627 570 540 430 387 387 379 4701
93.8 106.0 104.5 95.0 90.0 95.6 86.0 86.0 84.2 97.9
554 606 612 543 468 312 568 371 353 4387
98.4 95.3 97.6 95.3 86.7 72.6 99.8 95.9 93.1 93.3
Percentages calculated for the number of sampled subjects in each city. Percentages calculated for the number of interviewed subjects in each city.
The distribution of subjects in nine provinces is presented in Table 2 by several characteristics. The percentage of subjects under the 1 year of age was low due to the reasons mentioned above. Of subjects included in the study, 47.3% were male and 51.5% female. By family size, 64.3% had five or less family members and 34.6% had six or more family members. Of subjects, 65.3% were living in urban areas, 6.3% in suburban areas, and 28.4% in rural areas. Positive VZV seroprevalence was detected in 77.8% of 4387 subjects under age 30 in nine provinces of Turkey. Table 2 Several characteristics of subjects participating in VZV seroprevalence study in nine provinces, Turkey (1998) Characteristic Age 0 1–3 4–6 7–9 10–14 15–19 20–24 25–29 Unknown Total
Number
Table 3 shows the distribution of VZV seroprevalences by several subject characteristics. Although the average rate was around 75–80%, seroprevalence rates by provinces ranged from a low of 69.7% (Edirne) to a high of 83.6% (Diyarbakir). There was no difference in seroprevalence rate between rural and urban areas. Seroprevalence was found to be 79.0% in urban areas and 76.3% in rural areas. Seroprevalence increased with age. Seroprevalence was 20% at the age of 1 year, subsequently increased to 40% at the age of 4 years, 60% at 6 years of age, 80% at the age of 8 years, 85% at the age of 10 years, and then remained at 85–90% in subjects over the age of 10 years.
Percentage
57 495 503 513 864 746 611 546 52 4387
1.3 11.3 11.5 11.7 19.7 17.0 13.9 12.5 1.1 100
Table 3 Positive VZV seroprevalence for population under age 30 by several socio-demographic characteristics in nine cities of Turkey (1998) Characteristic
Number
Positive seroprevalence (%)
Age (n = 4335) 0 1–3 4–6 7–9 10–14 15–19 20–24 25–29
57 495 503 513 864 746 611 546
19.3 32.5 59.4 81.1 88.1 90.2 91.2 91.9
Sex (n = 4335) Male Female
2076 2259
76.0 79.7
Sex Male Female Unknown Total Family size Five and less Six and more Unknown Total
2076 2259 52 4387
47.3 51.5 1.2 100
2819 1518 50 4387
64.3 34.6 1.1 100
Family size (n = 4387) Five and less Six and more
2819 1518
78.1 80.6
Location Urban area Suburb Rural area Total
2863 279 1245 4387
65.3 6.3 28.4 100
Location Urban area Suburb Rural area Total
2863 279 1245 4387
79.0 74.8 76.3 77.8
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4. Discussion Varicella is an important health care problem because it is common throughout the world, is highly contagious and carries a high secondary attack rate [1]. In order to develop vaccination protocols and take appropriate preventive health care measures against diseases in different countries, it is very important to know the seroprevalence of any disease for an individual country. This study which was conducted using the 30 cluster sampling method in nine provinces of Turkey, including both rural and urban areas, providing a representative data for Turkey. The ratio of realized population to targeted population was 93.3%. In general, this figure was sufficient except for the age group under 1 year of age. The main reason for this was that blood sampling was not performed in children under the age one due to the difficulty of obtaining blood sample. When comparing various seropositivity studies, methods of antibody detection should be similar. We used ELISA method, currently the most accurate method, which is sensitive, specific and especially recommended for field studies [7,8]. The results of our study can be considered comparable with those in the literature [9–12]. Varicella seropositivity was 32.5% at the end of age 3, 59.4% at the end of age 6 and 81.1% at the end of age 9, and it was concluded that most of the cases occurred before age 10. When seropositivity was evaluated by age, seropositivity showed a linear increase from age 2 to age 10. At this point, it reaches a plateau showing only moderate increases with age. Seropositivity was already 88.1% at the end of age 14 and then increased to 92% at the age 30. Several studies in the literature have reported that varicella is most frequently seen between ages 4 and 10 [11,12]. However, several studies have reported that seropositivity ranges between 80 and 100% in adults [12,13]. It has been reported that the age at which people are infected for the first time is higher, and that this disease is more important for adults and adolescents in Asian countries [7]. In our study, there was no difference in seropositivity between sexes. Seropositivity rates were equivalent in rural and urban areas and among the nine provinces studied. Studies performed in other countries also support that there is no significant seropositivity difference between sex and race. [11,12]. However, seropositivity has been reported to be lower in adults living in rural areas than those living in urban areas [14].
The results of our study showed that varicella is a disease affecting the general population, causing infection regardless of sex and socio-economical class, and is highly common during the pre-school and primary school period. These results are similar to those of studies conducted in other countries. Based on the results of our study, it will be useful for Turkey to establish a childhood vaccination program.
Acknowledgements This study was supported by Glaxo-SmithKline. References [1] Weller TH. Varicella-Herpes Zoster. In: Evans AS, editor. Viral infections of humans. Epidemiology and Control. 3rd ed. London: Plenum Medical Book Co., 1991. [2] Benenson SA, editor. Control of communicable diseases in man. 15th ed. Washington DC: APHA publication, 1990. p. 83–86. [3] WHO. Expanded programme on immunization weekly. Epidemiol. Rec. 1984;39:297–300. [4] Rothenberg RB, Labanov A, Singh KB, Stroh Jr G. Observations on the application of EPI cluster survey methods for estimating disease incidence. Bull WHO 1985;63:93–9. [5] Henderson RH, Sunderasan T. Cluster sampling to assess immunization coverage: a review of experience with a simplified sampling method. Bull WHO 1982;60:2053–60. [6] Remington RD, Schark MA. Statistics with application to biological and health sciences. London: Prientice-Hall, 1970. [7] Gershon AA, Takahashi M, White C Jo. Varicella vaccine. In: Plotkin SA, Orenstein WA, editors. Vaccines. 3rd ed. Philadelphia: Saunders, 1999. p. 475–507. [8] Echevarria JM, Ory F, Leon P, Tellez A. Definition of high-proficiency serological markers for diagnosis of varicella-zoster virus infections by immunoassay. J Med Virol 1989;27:224–30. [9] Takahashi M, Okuno Y, Otsuka T. Live vaccine used to prevent the spread of varicella in children in hospital. Lancet 1974;2:1288– 90. [10] Committee on Infectious Diseases. Recommendations for the use of live attenuated varicella vaccine. Pediatrics 1995;95:791–96. [11] Muench R, Nassim C, Niku S, Sullivan-Bolyai JZ. Seroepidemiology of varicella. J Infect Dis 1986;153:153–5. [12] Eguiluz GC, Trallero EP, Arenza JMG. Seroedidemiology of varicella in children from Spain. J Infect Dis 1987;156:851. [13] Rivers TM, Eldridge LA. Relation of varicella to herpes zoster. I. Statistical observations. II. Clinical and experimental observations. J Exp Med 1929;49:899–917. [14] Alter SJ, Hammond JA, McVey CJ, Myers M. Susceptibility to varicella zoster virus among adults at high risk for exposure. Infect Contr 1986;7:448–51.
Varicella seroprevalence in a random sample of the Turkish population G. Kanra a,∗ , S. Tezcan b , S. Badur c , Turkish National Study Team1 a
Pediatric Infectious Disease Unit, Department of Pediatrics, Faculty of Medicine, Hacettepe University, 06100 Ankara, Turkey b Department of Public Health, Faculty of Medicine, Hacettepe University, Ankara, Turkey c Department of Microbiology, Faculty of Medicine, Istanbul University, Istanbul, Turkey Received 9 January 2001; received in revised form 20 September 2001; accepted 29 October 2001
Abstract Chicken pox highly contagious and common throughout the world, is an infectious disease caused by varicella zoster virus (VZV). This study was conducted to determine the seroprevalence of VZV in a population under age 30 and to identify the relationship of VZV seroprevalence and several characteristics of the study subjects in nine provinces of Turkey. The sampling method of 30 clusters recommended for field studies was used for selecting subjects of a pre-determined number in the rural and urban areas in each province. For this, a total of 60 groups, 30 clusters in the rural and 30 in the urban areas were determined. It was planned that a total of 4800 subjects, including 600 subjects from five big provinces (Istanbul, Ankara, Izmir, Adana, Diyarbakir) and 450 subjects from the remaining smaller provinces (Samsun, Erzurum, Trabzon, Edirne), be included in the study. ELISA method was used to examine the blood samples for VZV seropositivity. Positive VZV seroprevalence was detected in 77.8% of 4387 subjects under age 30 in nine provinces of Turkey. There was no difference in seroprevalence rate between rural and urban areas. Seroprevalence was found to be 79.0% in urban areas and 76.3% in rural areas. Seroprevalence increased with age. Seroprevalence was 20% at the age of 1 year, subsequently increased to 40% at the age of 4 years, 60% at the age 6 years, 80% at the age of 8 years, 85% at the age of 10 years, and then remained at 85–90% in subjects over the age of 10 years. In order to develop vaccination protocols and take appropriate preventive health care measures against diseases in different countries, it is very important to know the seroprevalence of any disease for an individual country. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: Varicella; Seroprevalance; Vaccine
1. Introduction Chicken pox is an infectious disease caused by varicella zoster virus (VZV). Ninety percent of all cases in the USA occur in children under the age of 15 years. The incidence of disease is similar in both sexes and different races. Virus from an infected person contaminates a healthy individual
via contact with fluids from skin lesions or droplets through respiratory system [1,2]. In general, life-long immunity develops following infection to chicken pox. This immunity depends on the antibody production as a result of cellular immunologic response. Cellular immunity may weaken with advancing age and the virus may be reactivated. Consequently, this reactivation
∗ Corresponding
author. Tel.: +90-312-3114963; fax: +90-312-3108241. H: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Atatürk University, Erzurum, Turkey. Bulut A: Professor of Public Health, Department of Pediatrics, Faculty of Medicine, Istanbul University, Istanbul, Turkey. Cin S: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ankara University, Ankara, Turkey. Çan G: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Karadeniz Technical University, Trabzon, Turkey. Dündar C: Pediatrician, Department of Pediatrics, Faculty of Medicine, 19 Mayis University, Samsun, Turkey. Egemen A: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ege University, Izmir, Turkey. Eskiocak M: Pediatrician, Department of Pediatrics, Faculty of Medicine, Trakya University, Ankara, Turkey. Evliyaoglu N: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Çukurova University, Adana Turkey. Güraksin A: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Atatürk University, Erzurum, Turkey. Mocan H: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Karadeniz Technical University, Trabzon, Turkey. Öztürk F: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, 19 Mayis University, Samsun, Turkey. Saka G: Pediatrician, Department of Pediatrics, Faculty of Medicine, Dicle University, Diyarbakir, Turkey. Sidal M: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Istanbul University, Istanbul, Turkey. Ulukol B: Associate Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Ankara University, Ankara, Turkey. Tanyer G: Professor of Pediatrics, Ankara Hospital, Ministry of Health, Ankara, Turkey. Tas MA: Professor of Pediatrics, Department of Pediatrics, Faculty of Medicine, Dicle University, Diyarbakir, Turkey. Yazicioglu M: Pediatrician, Department of Pediatrics, Faculty of Medicine, Trakya University, Edirne, Turkey. Dagbasi N: Glaxo-SmithKline Beecham, Istanbul, Turkey. Velicangil Ö: Glaxo-SmithKline Beecham, Istanbul, Turkey. 1 Alp
0264-410X/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 0 1 ) 0 0 4 5 9 - 5
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G. Kanra et al. / Vaccine 20 (2002) 1425–1428
leads to pain and vesicles on the dermatome of sensory nerves, presenting as herpes zoster infection. [1,2]. Chicken pox is not a notifiable disease in Turkey. Moreover, because Turkey has not conducted a community-based study on this disease, the exact incidence is not known. Therefore, we conducted a study to determine the seroprevalence of VZV in the population under age 30 and to identify the relationship between VZV seroprevalence and several characteristics of the study subjects in nine provinces of Turkey. The subjects and locations provide a representative sample of geographic, demographic and socio-economical characteristics of Turkey.
2. Materials and methods The present study of seroprevalence of VZV was conducted in nine provinces of Turkey. The sampling method of 30 clusters was used for selecting subjects of a pre-determined number in the rural and urban areas in each province. This is a practical method recommended by World Health Organisation for field studies [3–5]. For this, a total of 60 clusters in the rural (30 clusters) and urban (30 cluster) areas were determined and the related lists were sent to the principal investigator in each city. The provinces included were Istanbul, Ankara, Izmir, Adana, Diyarbakir, Samsun, Trabzon, Erzurum and Edirne. Because one-third of Turkish population live in these areas, we believe that the seroprevalence of study subjects would be highly representative of the entire country. In addition to providing a representative cross sample, these provinces also draw intense migration from neighbouring cities and communities farther away. In each province, sample sizes were determined from published data on varicella seroprevalance and sample size formula for cluster sample size for each group of subjects under age 30 for seroprevalence estimates within 95% confidence rate [6]. Therefore, it was planned that a total of 4800 subjects, including 600 subjects from five big provinces (Istanbul, Ankara, Izmir, Adana, Diyarbakir) and 450 subjects from the remaining smaller provinces (Samsun, Erzurum, Trabzon, Edirne), be included in the study. These number were distributed among 0–30 years of age population of each province proportional to the actual size. The age groups were separated in to 5-year groups. The number and distribution of population in each province was obtained from the State Institute of Statistics. When the investigators reached the cluster (villages in rural area and streets in urban area) the door number to start was chosen randomly. Then until the predetermined number in each age group is reached houses were visited. In order to provide a standard practice, investigators in each centre were appropriately trained on such issues as the selecting subjects, obtaining informed consent, applying the questionnaire, taking blood sample, and collecting, storing
and transporting sera for the serum. Additionally, the authorised ethics committee in each centre approved this seroprevalence study, and the entire study was pre-approved by the ethics committee of the Ministry of Health. Each potential subject who was interviewed and who agreed to participate read and signed a written informed consent form. A questionnaire about several characteristics of subjects was used to obtain data on VZV epidemiology (for their parents or guardians supplied those under age 18, information). Following the interviews, appropriate blood samples were taken from subjects for seroprevalence analyses. Serum analyses were performed at the Microbiology Laboratory of Istanbul University Faculty of Medicine. Serum samples were obtained from the blood samples and transported to the related laboratory in accordance with the principles of cold chain. For each serum sample, a quantitative investigation for anti-varicella virus-IgG (anti-VZV-IgG) antibodies was performed using Dade-Behring micro-ELISA kits (Dade Behring Marburgh, Germany). The sensitivity and specificity of the ELISA method is approved especially for the field studies [7,8]. All serum samples including controls and references were diluted by 1/10 and added to two separate cupules, one containing viral antigen and the other containing control antigen. Following an incubation period of 60 min at 37 ◦ C, cupules were irrigated three times so that the unbounded materials were removed, then peroxidase-labelled anti-human conjugate (100 l) was added to the cupules. Following incubation period of of 60 min at 37 ◦ C cupules were irrigated again, and the chromogen substrate was added to the cupules. The reaction occurring in ELISA plates stored at room temperature for 30 min was terminated by adding 100 l of stopper buffer solution to each cupule. Subsequently, absorbency value for each cupule was detected by reading at 450 nm. By considering the absorbency values for cupules covered with or without antigen and using ␣-method, anti-VZV-IgG level was quantitatively determined for each serum sample. As this was a descriptive study only percentages were calculated and no further statistical analysis was made.
3. Results This seroprevalence study included a total of 4461 subjects representative of the population under age 30 in nine provinces of Turkey (Table 1). In Ankara, Izmir and Erzurum, more subjects than targeted sample size were questioned and subjected to blood analysis. The size of participation was also larger than expected, representing the population in related provinces. Generally, seroprevalences could not be determined in 5.1% of sampled subjects and 6.7% of interviewed subjects. The main reason for this was that blood sampling could not be performed in children under 1 year of age due to the difficulty of obtaining blood sample.
G. Kanra et al. / Vaccine 20 (2002) 1425–1428
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Table 1 Distribution of subjects selected for sampling, interviewed and underwent blood sampling in nine provinces (Turkey 1998) Provinces
Istanbul Ankara Izmir Adana Diyarbakir Samsun Erzurum Trabzon Edirne Total a b
Number of sampled subjects
600 600 600 600 600 450 450 450 450 4800
Positive seroprevalence
Number of interviewed subjects
79.8 78.2 73.2 80.9 83.6 75.8 76.9 78.2 69.7 77.8
Number of subjects undergoing blood analysis
Number
Percentagea
Number
Percentageb
563 636 627 570 540 430 387 387 379 4701
93.8 106.0 104.5 95.0 90.0 95.6 86.0 86.0 84.2 97.9
554 606 612 543 468 312 568 371 353 4387
98.4 95.3 97.6 95.3 86.7 72.6 99.8 95.9 93.1 93.3
Percentages calculated for the number of sampled subjects in each city. Percentages calculated for the number of interviewed subjects in each city.
The distribution of subjects in nine provinces is presented in Table 2 by several characteristics. The percentage of subjects under the 1 year of age was low due to the reasons mentioned above. Of subjects included in the study, 47.3% were male and 51.5% female. By family size, 64.3% had five or less family members and 34.6% had six or more family members. Of subjects, 65.3% were living in urban areas, 6.3% in suburban areas, and 28.4% in rural areas. Positive VZV seroprevalence was detected in 77.8% of 4387 subjects under age 30 in nine provinces of Turkey. Table 2 Several characteristics of subjects participating in VZV seroprevalence study in nine provinces, Turkey (1998) Characteristic Age 0 1–3 4–6 7–9 10–14 15–19 20–24 25–29 Unknown Total
Number
Table 3 shows the distribution of VZV seroprevalences by several subject characteristics. Although the average rate was around 75–80%, seroprevalence rates by provinces ranged from a low of 69.7% (Edirne) to a high of 83.6% (Diyarbakir). There was no difference in seroprevalence rate between rural and urban areas. Seroprevalence was found to be 79.0% in urban areas and 76.3% in rural areas. Seroprevalence increased with age. Seroprevalence was 20% at the age of 1 year, subsequently increased to 40% at the age of 4 years, 60% at 6 years of age, 80% at the age of 8 years, 85% at the age of 10 years, and then remained at 85–90% in subjects over the age of 10 years.
Percentage
57 495 503 513 864 746 611 546 52 4387
1.3 11.3 11.5 11.7 19.7 17.0 13.9 12.5 1.1 100
Table 3 Positive VZV seroprevalence for population under age 30 by several socio-demographic characteristics in nine cities of Turkey (1998) Characteristic
Number
Positive seroprevalence (%)
Age (n = 4335) 0 1–3 4–6 7–9 10–14 15–19 20–24 25–29
57 495 503 513 864 746 611 546
19.3 32.5 59.4 81.1 88.1 90.2 91.2 91.9
Sex (n = 4335) Male Female
2076 2259
76.0 79.7
Sex Male Female Unknown Total Family size Five and less Six and more Unknown Total
2076 2259 52 4387
47.3 51.5 1.2 100
2819 1518 50 4387
64.3 34.6 1.1 100
Family size (n = 4387) Five and less Six and more
2819 1518
78.1 80.6
Location Urban area Suburb Rural area Total
2863 279 1245 4387
65.3 6.3 28.4 100
Location Urban area Suburb Rural area Total
2863 279 1245 4387
79.0 74.8 76.3 77.8
1428
G. Kanra et al. / Vaccine 20 (2002) 1425–1428
4. Discussion Varicella is an important health care problem because it is common throughout the world, is highly contagious and carries a high secondary attack rate [1]. In order to develop vaccination protocols and take appropriate preventive health care measures against diseases in different countries, it is very important to know the seroprevalence of any disease for an individual country. This study which was conducted using the 30 cluster sampling method in nine provinces of Turkey, including both rural and urban areas, providing a representative data for Turkey. The ratio of realized population to targeted population was 93.3%. In general, this figure was sufficient except for the age group under 1 year of age. The main reason for this was that blood sampling was not performed in children under the age one due to the difficulty of obtaining blood sample. When comparing various seropositivity studies, methods of antibody detection should be similar. We used ELISA method, currently the most accurate method, which is sensitive, specific and especially recommended for field studies [7,8]. The results of our study can be considered comparable with those in the literature [9–12]. Varicella seropositivity was 32.5% at the end of age 3, 59.4% at the end of age 6 and 81.1% at the end of age 9, and it was concluded that most of the cases occurred before age 10. When seropositivity was evaluated by age, seropositivity showed a linear increase from age 2 to age 10. At this point, it reaches a plateau showing only moderate increases with age. Seropositivity was already 88.1% at the end of age 14 and then increased to 92% at the age 30. Several studies in the literature have reported that varicella is most frequently seen between ages 4 and 10 [11,12]. However, several studies have reported that seropositivity ranges between 80 and 100% in adults [12,13]. It has been reported that the age at which people are infected for the first time is higher, and that this disease is more important for adults and adolescents in Asian countries [7]. In our study, there was no difference in seropositivity between sexes. Seropositivity rates were equivalent in rural and urban areas and among the nine provinces studied. Studies performed in other countries also support that there is no significant seropositivity difference between sex and race. [11,12]. However, seropositivity has been reported to be lower in adults living in rural areas than those living in urban areas [14].
The results of our study showed that varicella is a disease affecting the general population, causing infection regardless of sex and socio-economical class, and is highly common during the pre-school and primary school period. These results are similar to those of studies conducted in other countries. Based on the results of our study, it will be useful for Turkey to establish a childhood vaccination program.
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