Case-Control Study of Conjunctival Bacterial Infection in Trachomatous Scarring

Abstract

Purpose: : Trachoma is the most common infectious cause of blindness globally. Repeated episodes of infection with Chlamydia trachomatis in childhood cause conjunctival inflammation and trigger cicatricial complications. The factors driving the scarring process in adults remain uncertain as infection with C. trachomatis is rarely found. One factor which may be important is non-chlamydial bacterial infection. The purpose of this study was to determine the frequency and type of infection in subjects with trachomatous scarring compared to controls.

Methods: : A case-control study was conducted in a trachoma endemic area of Northern Tanzania. Adults with trachomatous conjunctival scarring and control subjects without scarring were recruited from the same communities. Conjunctival scarring and inflammation were graded. A conjunctival swab sample was collected and placed immediately into Amies transport media at room temperature. Samples were inoculated onto blood and chocolate agar an average of 4 hours later and incubated for 48 hours. Culture isolates were identified by standard microbiological techniques.

Results: : 362 cases and 362 controls were recruited. Sex and ethnic group composition was similar. Cases were older than controls. Staphylococcus epidermidis, Corynebacteria and Streptococcus viridans were considered commensal. Other bacteria were defined as pathogens. Conjunctival inflammation was associated with pathogens but not commensals. Scarring was associated with pathogens and to a lesser extent, commensals. Multivariable logistic regression showed scarring to be associated with age (OR 2.07 for each increase in 10-year age group; 95% CI=1.81-2.37; p-value <0.001), lack of education (OR 0.37 if any education; 95%=CI 0.27-0.50; p-value <0.001), commensal organisms (OR 1.46; 95% CI 1.01-2.12; p-value 0.04) and pathological organisms (OR 2.81; 95% CI=1.39-5.69; p-value=0.004).

Conclusions: : Conjunctival scarring is significantly associated with the presence of non-Chlamydial bacterial infection. This infection provokes an inflammatory response which may contribute to the scarring process. The role for antibiotic treatment of this infection warrants investigation.

Keywords: trachoma • bacterial disease • conjunctiva