Ghaza Haq  ( PMRC Research Centre, Jinnah Postgraduate Medic Centre, Karachi. )

In the 1970’s important contributions were made to the understanding of infectious diseases and many developments were made in bacteriology. During 1970 Legionella pneumophila was discovered which was the etiologic agent of Legionnaires disease (Brenner et ., 1979). This was first isolated from the lungs of 4 patients who had Legionnaires disease in association with the 1976 Philadelphia outbreak (McDade et al., 1979).
L.pneumophila has been isolated from a variety of environment samples most of which are wet. In the laboratory L. pneumophila has been demonstrated to survive for prolonged periods in distilled and tap water.
Members of the genus legionella are gram negative, aerobic non spore-forming bacilli that do not grow or grow very slowly, on ordinary laboratory medium. They are typicly 0.5 to 0.74 in width and 2 - 204 in length. On initi culture (passage on growth supporting mediums) L. pneumophila organisms as well as other legionellae when stained with Sudan black B fat stain, appear pink and have slightly swollen regions that contain either blue black or grey blue droplets (Weaver and Feeley, 1979). Cystiene HCL and hemoglobin are important chemics required for growth at optimum pH 6.90. Hemoglobin which served as an iron source can so be supplied by soluble ferric pyrophosphate (Feeley et at., 1978).
L.pneumophila has been estimated to cause 25,000 cases of pneumonia in the United States each year or 1% of l cases of pneumonia (Foy et at., 1979). Nineteen epidemics of legionollosis have been investigated by the centre for disease control and l out-breaks were caused by L. pneumophila. Typicly, epidemic legionollosis occurs in early summer and fl. Sporadic legionollosis has occurred since 1947 (McDade et al., 1979) and is recognized world wide.
The incubation period of legionollosis has been identified only in ielation to out breaks, and is said to vary from 2 - 10 days (Fraser et at., 1977).
The pattern of sever outbreaks is consistent with airborne spread, despite intensive efforts to document secondary spread no convincing evidence for person to person transmission of legionollosis has been established. Risk of legionollosis tends to increase among middle age and elderly men, coholics, those on immunosuppressive drugs or any other disease.
l measures at present to prevent legionollosis or dissemination of L. pneumophila from the environment has failed. Major unsolved problems regarding the epidemiology of legionollosis involve understanding of the sources of acquisition and mode of spread in sporadic disease, environment factors responsible for the growth and dissemination of legionella organisms, and means for its prevention. Preliminary studies have demonstrated that a purified antigen isolated from L. pneumophila causes delayed skin reactions in previously sensitized guinea pigs (Wong et ., 1979). Development of a skin test for use in humans could enhance the understanding of how sporadic legionollosis is acquired. Prevention might be achieved by developing an effective vaccine (Wonget., 1979).
The diagnosis of legionollosis can be confirmed by the demonstration of a 4 fold rise in indirect fluorescent antibody titer 7,128 or by demonstration of the organisms by direct fluorescent antibody staining or by the isolation of the organisms (Soravolatz, 1979; Broome et aL, 1979; FeeIey et al., 1979; Edeistein et al., 1979) Pneumonia being quite common in our patient population, it is therefore suggested that doubtful cases should undergo screening for legionnaires disease.

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