Correspondence

Single-Dose Azithromycin for Trachoma

N Engl J Med 2005; 352:414-415January 27, 2005

Article

To the Editor:

Solomon et al. (Nov. 4 issue)1 suggest that the ocular chlamydia that causes trachoma can be eliminated by a single mass antibiotic treatment. Two years after distributing oral azithromycin in a village, they identified only a single infection. The authors state that this finding “contrasts starkly” with the prediction of our mathematical model.2,3 Yes and no. We do predict that infection will eventually return after a single mass treatment. However, with 97.5 percent coverage of a moderately infected area, this return may take a long time. Our model predicts that less than 3 percent of persons will be infected at one year — and an even smaller proportion in this case, since Solomon et al. also distributed tetracycline ointment. Furthermore, this estimate is only an expectation (or average), and chance can have a large effect. We recently monitored 24 villages in Ethiopia after a single mass treatment; in some villages, infection was eliminated at two months, and in others it returned relatively rapidly.3 Unfortunately, the evidence so far suggests that, on average, infection returns after a single mass treatment, but to test this properly, one must look at more than one village.

Thomas M. Lietman, M.D.
Bruce Gaynor, M.D.
University of California, San Francisco, San Francisco, CA 94143-0944
tml@itsa.ucsf.edu

Travis Porco, Ph.D.
California Department of Health Services, Berkeley, CA 94704

3 References

1. 1

   Solomon AW, Holland MJ, Alexander NDE, et al. Mass treatment with single-dose azithromycin for trachoma. N Engl J Med 2004;351:1962-1971
   Full Text | Web of Science | Medline

2. 2

   Lietman T, Porco T, Dawson C, Blower S. Global elimination of trachoma: how frequently should we administer mass chemotherapy? Nat Med 1999;5:572-576
   CrossRef | Web of Science | Medline

3. 3

   Melese M, Chidambaram JD, Alemayehu W, et al. Feasibility of eliminating ocular Chlamydia trachomatis with repeat mass antibiotic treatments. JAMA 2004;292:721-725
   CrossRef | Web of Science | Medline

Author/Editor Response

Two main factors differentiate our study from the model of Lietman et al.1 First, our primary outcome measure was an adjusted geometric mean of the ocular Chlamydia trachomatis load, determined with the use of a quantitative polymerase-chain-reaction assay. The model, in contrast, used the prevalence of active trachoma, which correlates poorly with chlamydial infection.2 Second, we reported that after high-coverage mass treatment, the load of infection dropped and then continued to fall for at least two years, whereas the model predicted that (in communities like ours, where the disease is mesoendemic) the prevalence of disease would double every four to eight months after a treatment-induced fall. Our results suggest that there may be a threshold level of infection, below which the transmission of trachoma ceases; its return might then depend on reintroduction from the outside by persons with heavy shedding of C. trachomatis. We agree that our data are from only a single community case study but note that six months after mass treatment, six Ethiopian villages studied by Lietman's group had a prevalence of infection of 0 percent.3 Modeling with the use of quantitative infection data would be a useful next step.

Anthony W. Solomon, M.B., B.S., Ph.D.
Allen Foster, F.R.C.S., F.R.C.Ophth.
David C.W. Mabey, D.M., F.R.C.P.
London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom
anthony.solomon@lshtm.ac.uk

3 References

1. 1

   Lietman T, Porco T, Dawson C, Blower S. Global elimination of trachoma: how frequently should we administer mass chemotherapy? Nat Med 1999;5:572-576
   CrossRef | Web of Science | Medline

2. 2

   Solomon AW, Peeling RW, Foster A, Mabey DC. Diagnosis and assessment of trachoma. Clin Microbiol Rev 2004;17:982-1011
   CrossRef | Web of Science | Medline

3. 3

   Melese M, Chidambaram JD, Alemayehu W, et al. Feasibility of eliminating ocular Chlamydia trachomatis with repeat mass antibiotic treatments. JAMA 2004;292:721-725
   CrossRef | Web of Science | Medline