Non-tuberculosis mycobacteria in Africa. 1. Isolation and identification

Abstract

In tropical and subtropical countries, the presence of non-tuberculosis mycobacteria may invalidate case-finding programmes; experience has shown that many of the acid-fast bacilli discovered on examination of sputum specimens are non-tuberculosis mycobacteria-either photochromogens, scotochromogens, unpigmented or rapid growers (Groups I to IV, respectively, of Runyon's classification) or saprophytes.Studies have recently been undertaken to determine the frequency of various types of non-tuberculosis strains in different parts of Africa. This paper describes the first of these studies, devoted to the isolation and identification of non-tuberculosis mycobacteria from seven countries.Of 18 568 cultures examined at the Central Tuberculosis Laboratory, Nairobi, in 1961-64, 1.9% were non-tuberculosis strains. However, valid conclusions as to prevalence cannot be drawn from this figure, since some specimens came from tuberculosis patients and others from general population surveys. An earlier comparison, based on 7580 cultures from tuberculosis patients and 657 from a random survey, had shown a significant difference in the frequency of non-tuberculosis strains, the figures being 1.1% and 19.8%, respectively.Of the identification tests studied, the formamidase test was found very useful for differentiating saprophytic mycobacteria from the other non-tuberculosis mycobacteria, particularly the rapid growers. This test is discussed in greater detail in the third study of the series.