Clinical examination and laboratory tests for estimation of trachoma prevalence in remote settings – Authors' reply

Abstract

We agree with Anthony Solomon and colleagues that there are a number of reasons for the discrepancies between nucleic acid amplification tests (NAATs) and clinical grading of trachoma. Individuals who are NAAT positive in the absence of clinical signs may represent an incubation or latent stage. However, as figures 7, 8, and 9 of our paper 1 Wright HR Taylor HR Clinical examination and laboratory tests for estimation of trachoma prevalence in a remote setting: what are they really telling us?. Lancet Infect Dis. 2005; 5: 313-320 Summary Full Text Full Text PDF PubMed Scopus (62) Google Scholar show, this phase might be quite brief. In the monkey model, clinical signs were generally present within 1–2 weeks of inoculation. 2 Taylor HR Johnson SL Prendergast RA Schachter J Dawson CR Silverstein AM An animal model of trachoma II. The importance of repeated reinfection. Invest Ophthalmol Vis Sci. 1982; 23: 507-515 PubMed Google Scholar Therefore, although a latent state may account for some clinically normal people who are NAAT positive; it is probably not sufficient to explain all the data. Potential contamination of samples in the field must also be considered. Figure 5 in our paper 1 Wright HR Taylor HR Clinical examination and laboratory tests for estimation of trachoma prevalence in a remote setting: what are they really telling us?. Lancet Infect Dis. 2005; 5: 313-320 Summary Full Text Full Text PDF PubMed Scopus (62) Google Scholar shows that in communities with hyperendemic levels of trachoma, approximately 20% of clinically normal individuals are NAAT positive. Unfortunately, only one of these studies describes methodology designed to minimise the possibility of contamination. However, even these precautions might not be considered adequate, consisting of hand washing and preventing the swab head from contacting anything other than the subject's conjunctiva. 3 Solomon AW Holland MJ Burton MJ et al. Strategies for control of trachoma: observational study with quantitative PCR. Lancet. 2003; 362: 198-204 Summary Full Text Full Text PDF PubMed Scopus (171) Google Scholar To be confident that contamination is not an issue, a minimum requirement should be that both the examiner (everting the lids) and the collector (doing the swab) wear gloves and mask. Unless these standard precautions are taken, the real issue of potential sample contamination must be considered and we should be cautious about adopting new biological explanations based on these data. Clinical examination and laboratory tests for estimation of trachoma prevalence in remote settingsWe would like to commend Heathcote Wright and Hugh Taylor1 for their comprehensive review of trachoma in remote settings, which is an important global health issue. We agree with the authors' explanation of the well-known discordance between clinical signs and the actual infective status as well as the emphasis on clinical assessment. However, the role of PCR in supplementing trachoma intervention, particularly in hypoendemic areas, may not have been adequately illustrated. Full-Text PDF