Performance of the Ogawa-Kudoh method for isolation of mycobacteria in a laboratory with large-scale workload

In Uruguay (population 3,323,906; notified tuberculosis incidence 18.4/100,000), virtually all 30,000 samples yearly collected for mycobacterial culture countrywide are processed in a central laboratory. An average of 110 samples are routinely shipped daily and maintained 48-96 hours at room temperature until cultured on Löwenstein-Jensen slants using the standard NALC-NaOH decontamination procedure. The much simpler Kudoh decontamination/culture method -swab and Ogawa (acidified) medium- was compared with NALC-NaOH/Löwenstein-Jensen for isolation of mycobacteria from sputa under routine conditions. To this aim, 784 sputum samples were cultured by both methods in the summertime. Gross agreement was 0.99, kappa: 1. Kudoh performance was as follows: sensitivity 100% and accuracy 98.9%. Assays using a modified culture medium, different decontamination times and NaOH concentrations showed the versatility of this procedure. Thus, the Kudoh method is suitable for culturing mycobacteria from naturally contaminated samples even when processing is deferred two to four days after collection.