- Email: [email protected]
Trachoma research: it takes more than a village
Correspondence
We declare that we have no conflict of interest.
*Charles Shey Wiysonge, Emmanuel Nomo, Jeanne Ngo-Ndjan Mawo, Johnson M Ticha [email protected] Expanded Programme on Immunisation, Ministry of Public Health, Yaoundé, Cameroon (CSW, EM, JNM); Division of Cardiology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa (CSW); and WHO Representative’s Office, Yaoundé, Cameroon (JMT) 1
2
3
Otten M, Kezaala R, Fall A, et al. Public-health impact of accelerated measles control in the WHO African Region 2000–03. Lancet 2005; 366: 832–39. Mills A. Mass campaigns versus general health services: what have we learnt in 40 years about vertical versus horizontal approaches? Bull World Health Organ 2005; 83: 315–16. Measles Initiative. http://www.measlesinitiative. org (accessed Sep 8, 2005).
Trachoma research: it takes more than a village Sheila West and colleagues (Oct 8, p 1296)1 monitored ocular chlamydial infection in a trachoma-endemic village in Tanzania after a single mass antibiotic treatment. The prevalence fell from 57% before treatment to 12% 2 months later. Over the next 16 months, levels bounced between 10% and 20% but never approached baseline. West and colleagues suggest that this finding contrasts with our mathematical model based on data from Ethiopia, which predicted that “re-emergence would arise to almost pre-treatment levels by 1 year after a single mass treatment”.2 Our simple model does indeed predict that, in the absence of retreatment and in the absence of a secular trend, infection should eventually return to baseline levels.3 However, this may take a long time. We predicted that, at 1 year, the prevalence would return only to 20%—ie, about a third of that found before treatment (figure).2 www.thelancet.com Vol 367 February 4, 2006
Furthermore, our estimate is only an expectation, or average. Stochastic models suggest that we should expect to see a large variation between villages, and also a large variation in the same village over time.4 Previously, we monitored 24 Ethiopian villages after a single mass treatment: infection disappeared from preschool children in some villages, hovered below 20% in others, and returned quite rapidly by 12 months in others (figure).2,5 Although it is tempting to suppose that there are striking differences between these Ethiopian villages, they had a similar pretreatment prevalence and were located within a few kilometres of each other. Much of the difference could just have been due to chance.2,4,5 Whatever the case, a study limited to only one of these villages would have produced completely different results from that of another. Recommendations on community treatment have to be made after studying numerous communities.2 West and colleagues also state that, in mesoendemic areas, “ocular infection with Chlamydia trachomatis can be eliminated after one mass treatment with antibiotics”. This statement is misleading. In epidemiology, elimination of infection means that incidence has been reduced to zero in a defined geographical area. Infection has probably been eliminated in some hypoendemic villages in Nepal and The Gambia, but it is difficult to attribute these results to the long-term effect of a single antibiotic distribution, since disease was probably disappearing on its own.5 Ocular chlamydia was reduced to a single case after several treatments in one mesoendemic village in Nepal and another in Tanzania.5 A single distribution eliminated infection from preschool children in a fortunate few of the 24 hyperendemic villages in Ethiopia mentioned above, although on average it clearly returned.2 Trachoma research is difficult. Severely affected communities are now found only in the poorest regions of the most undeveloped countries. It is impressive that a single village in rural
60 Example village 1
50 Prevalence of infection (%)
for the Measles Initiative3 and national governments to synchronise catch-up mass measles campaigns in the remaining countries with the follow-up campaigns in countries that have already conducted catch-up campaigns.
40 30
Average of all villages
20 10 Example village 2 0 0
1 Time after treatment (years)
2
Figure: Prevalence of Chlamydia trachomatis infection in 24 Ethiopian villages after a single mass azithromycin distribution Circles represent empirical data, solid curves interpolations, and dashed curves future projections. Adapted from reference 5.
Tanzania has received such research attention. However, community treatment recommendations cannot be based on studies of a single village, for the simple reason that different studies would provide entirely different recommendations. Long-term effects of single, annual, and biannual antibiotic distributions need to be tested, but to do so properly, it takes more than a village. We declare that we have no conflict of interest.
*Thomas M Lietman, Melissa D Neuwelt, Nandini G Gandhi, Cyril A Dalmon, Nicole Benitah [email protected] FI Proctor Foundation, Room S309, 513 Parnassus Avenue, University of California San Francisco, San Francisco, CA 94143, USA (TML); and School of Medicine, University of California San Francisco, San Francisco, CA, USA (MDN, NGG, CAD, NB) 1
2
3
4
5
West SK, Munoz B, Mkocha H, et al. Infection with Chlamydia trachomatis after mass treatment of a trachoma hyperendemic community in Tanzania: a longitudinal study. Lancet 2005; 366: 1296–300. Melese M, Chidambaram JD, Alemayehu W, et al. Feasibility of eliminating ocular Chlamydia trachomatis with repeat mass antibiotic treatments. JAMA 2004; 292: 721–25. Lietman T, Porco T, Dawson C, Blower S. Global elimination of trachoma: how frequently should we administer mass chemotherapy? Nat Med 1999; 5: 572–76. Lee DC, Chidambaram JD, Porco TC, Lietman TM. Seasonal effects in the elimination of trachoma. Am J Trop Med Hyg 2005; 72: 468–70. Chidambaram JD, Lee DC, Porco TC, Lietman TM. Mass antibiotics for trachoma and the Allee effect. Lancet Infect Dis 2005; 5: 194–96.
395
We declare that we have no conflict of interest.
*Charles Shey Wiysonge, Emmanuel Nomo, Jeanne Ngo-Ndjan Mawo, Johnson M Ticha [email protected] Expanded Programme on Immunisation, Ministry of Public Health, Yaoundé, Cameroon (CSW, EM, JNM); Division of Cardiology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa (CSW); and WHO Representative’s Office, Yaoundé, Cameroon (JMT) 1
2
3
Otten M, Kezaala R, Fall A, et al. Public-health impact of accelerated measles control in the WHO African Region 2000–03. Lancet 2005; 366: 832–39. Mills A. Mass campaigns versus general health services: what have we learnt in 40 years about vertical versus horizontal approaches? Bull World Health Organ 2005; 83: 315–16. Measles Initiative. http://www.measlesinitiative. org (accessed Sep 8, 2005).
Trachoma research: it takes more than a village Sheila West and colleagues (Oct 8, p 1296)1 monitored ocular chlamydial infection in a trachoma-endemic village in Tanzania after a single mass antibiotic treatment. The prevalence fell from 57% before treatment to 12% 2 months later. Over the next 16 months, levels bounced between 10% and 20% but never approached baseline. West and colleagues suggest that this finding contrasts with our mathematical model based on data from Ethiopia, which predicted that “re-emergence would arise to almost pre-treatment levels by 1 year after a single mass treatment”.2 Our simple model does indeed predict that, in the absence of retreatment and in the absence of a secular trend, infection should eventually return to baseline levels.3 However, this may take a long time. We predicted that, at 1 year, the prevalence would return only to 20%—ie, about a third of that found before treatment (figure).2 www.thelancet.com Vol 367 February 4, 2006
Furthermore, our estimate is only an expectation, or average. Stochastic models suggest that we should expect to see a large variation between villages, and also a large variation in the same village over time.4 Previously, we monitored 24 Ethiopian villages after a single mass treatment: infection disappeared from preschool children in some villages, hovered below 20% in others, and returned quite rapidly by 12 months in others (figure).2,5 Although it is tempting to suppose that there are striking differences between these Ethiopian villages, they had a similar pretreatment prevalence and were located within a few kilometres of each other. Much of the difference could just have been due to chance.2,4,5 Whatever the case, a study limited to only one of these villages would have produced completely different results from that of another. Recommendations on community treatment have to be made after studying numerous communities.2 West and colleagues also state that, in mesoendemic areas, “ocular infection with Chlamydia trachomatis can be eliminated after one mass treatment with antibiotics”. This statement is misleading. In epidemiology, elimination of infection means that incidence has been reduced to zero in a defined geographical area. Infection has probably been eliminated in some hypoendemic villages in Nepal and The Gambia, but it is difficult to attribute these results to the long-term effect of a single antibiotic distribution, since disease was probably disappearing on its own.5 Ocular chlamydia was reduced to a single case after several treatments in one mesoendemic village in Nepal and another in Tanzania.5 A single distribution eliminated infection from preschool children in a fortunate few of the 24 hyperendemic villages in Ethiopia mentioned above, although on average it clearly returned.2 Trachoma research is difficult. Severely affected communities are now found only in the poorest regions of the most undeveloped countries. It is impressive that a single village in rural
60 Example village 1
50 Prevalence of infection (%)
for the Measles Initiative3 and national governments to synchronise catch-up mass measles campaigns in the remaining countries with the follow-up campaigns in countries that have already conducted catch-up campaigns.
40 30
Average of all villages
20 10 Example village 2 0 0
1 Time after treatment (years)
2
Figure: Prevalence of Chlamydia trachomatis infection in 24 Ethiopian villages after a single mass azithromycin distribution Circles represent empirical data, solid curves interpolations, and dashed curves future projections. Adapted from reference 5.
Tanzania has received such research attention. However, community treatment recommendations cannot be based on studies of a single village, for the simple reason that different studies would provide entirely different recommendations. Long-term effects of single, annual, and biannual antibiotic distributions need to be tested, but to do so properly, it takes more than a village. We declare that we have no conflict of interest.
*Thomas M Lietman, Melissa D Neuwelt, Nandini G Gandhi, Cyril A Dalmon, Nicole Benitah [email protected] FI Proctor Foundation, Room S309, 513 Parnassus Avenue, University of California San Francisco, San Francisco, CA 94143, USA (TML); and School of Medicine, University of California San Francisco, San Francisco, CA, USA (MDN, NGG, CAD, NB) 1
2
3
4
5
West SK, Munoz B, Mkocha H, et al. Infection with Chlamydia trachomatis after mass treatment of a trachoma hyperendemic community in Tanzania: a longitudinal study. Lancet 2005; 366: 1296–300. Melese M, Chidambaram JD, Alemayehu W, et al. Feasibility of eliminating ocular Chlamydia trachomatis with repeat mass antibiotic treatments. JAMA 2004; 292: 721–25. Lietman T, Porco T, Dawson C, Blower S. Global elimination of trachoma: how frequently should we administer mass chemotherapy? Nat Med 1999; 5: 572–76. Lee DC, Chidambaram JD, Porco TC, Lietman TM. Seasonal effects in the elimination of trachoma. Am J Trop Med Hyg 2005; 72: 468–70. Chidambaram JD, Lee DC, Porco TC, Lietman TM. Mass antibiotics for trachoma and the Allee effect. Lancet Infect Dis 2005; 5: 194–96.
395