Improved tuberculosis smear detection in resource-limited settings: Combined bleach concentration and LED fluorescence microscopy

Improved diagnostics for tuberculosis is a high priority in resource-limited settings (RLS). Sputum concentration and fluorescence microscopy (FM) are standard techniques in developed countries where appropriate biosafety precautions are possible. Recently, inexpensive fluorescent lenses using LED light sources have made auramine-based FM more feasible in RLS. Sterilization of sputum with bleach protects lab personnel and, combined with concentration, increases the sensitivity of microscopic detection. We compared the effect of both bleach concentration and FM with LED based lenses to culture for the detection of tuberculosis in military medical hospitals in Addis Ababa, Ethiopia. Three sputum specimens were obtained from 409 patients (1227 total). Standard Ziehl-Neelsen (ZN) or auramine staining were compared with direct or bleach-concentrated specimens. The prevalence by culture was 26%. Sensitivity of microscopic diagnosis was increased both by bleach concentration (14%) and auramine staining (5%). The overall yield of smear positivity varied from 21% for direct ZN to 27% for auramine after concentration (P<0.00001, Cochran test for matched proportions). Twenty-nine HIV+ patients were diagnosed with TB, but ten (34%), would have been missed with direct ZN staining. Bleach concentration and auramine staining with new LED fluorescent systems are cost-effective and safe methods to increase the diagnostic yield of smears, including in HIV-infected patients.