All infants and children from four communities located in the Kongwa District of central Tanzania were selected for the study. A household census was conducted in these communities in 2009. Children aged <10 years were identified and their parent or guardian was invited to have their child participate in a longitudinal study of trachoma and infection over a three-year period. When available, maternal and child health cards allowed for the determination of exact birth date. When unavailable, infants' ages were determined in reference to village events in the past year, categorized as likely aged 6 months and older, and likely aged 6 months and younger.
Detailed study methods on the ocular examination and specimen analysis are described elsewhere.4
In summary, trained trachoma graders performed an ocular examination using 2.5× loupes and a torch to determine active trachoma. The trachoma graders were standardized during a 2 week training exercise before the start of the study. Interobserver agreement, and agreement with a senior grader had to be above kappa = 0.6 for TF and inflammatory trachoma (TI). Graders are monitored every 6 months by comparison of grades against the senior grader using a series of trachoma images.4
Active trachoma was graded using the World Health Organization simple grading scheme.5
An eyelid-conjunctival swab was obtained to assess infection with C. trachomatis. These swabs were taken using strict protocols to avoid contamination. Both the trachoma grader and eyelid flipper used gloves and changed them between each child examined. In addition, “air control” swabs were taken on a random sample of 5% of children. The swabs were waved in the air above the child but do not touch anything, marked as per any other sample, and sent for processing. If positive, further investigations were carried out to determine the source of contamination. The samples were kept at −20°C until they were sent to the International Chlamydia Laboratory at Johns Hopkins University for processing. The samples were analyzed using polymerase chain reaction (Amplicor; Roche Molecular Systems, Indianapolis, IN) according to manufacturer's directions. Optical density was used to identify positive results and defined as >0.7. Optical densities between 0.2 and 0.7 were considered equivocal and were retested. Results of these “air control” swabs showed some evidence of laboratory contamination that affected 34 samples at baseline. These contaminated samples were excluded; all further tests for contamination were negative at baseline and follow-up.
At the time of MDA, parents of infants aged <6 months were provided with tubes of 1% topical tetracycline with instruction to administer 1 to 2 times a day for 6 weeks. Children aged greater than 6 months were given a single dose of azithromycin (20 mg/kg up to 1 g). Community treatment assistants directly observed treatment with azithromycin; however, compliance with topical tetracycline was not monitored. Children and infants were re-evaluated at 6 months for the presence of active trachoma and C. trachomatis.
The association between infection in children at 6 months and presence of infants in the house was examined using a logistic model with infection as the outcome and presence of infants in the house as the predictor; the model accounted for the clustering of infection within children residents of the same household. An expanded model of infection was used to examine the independent contribution of age, sex, baseline chlamydial infection, and treatment at baseline, as well as presence of infants in the household. Odds ratios (ORs) and 95% confidence intervals (CIs) are presented where the generalized estimating equation (GEE) approach was used to correct the standard errors to account for the correlation among members of the same house, using the procedure GENMOD in SAS (Cary, NC) with binomial distribution, logit link function, and exchangeable correlation structure.
Written informed consent was obtained at the time of examination from all parents or guardians of children in the study. All procedures for the study were approved by the Johns Hopkins University Institutional Review Board (JHU IRB) and the National Institute of Medical Research (NIMR) in Tanzania and conducted in accordance with the Declaration of Helsinki.