Quantitative bacteriology of Typhoid fever in Vietnam

There is paucity of information on the number of bacteria in the blood and bone marrow of typhoid patients, and the relationship between bacterial load and clinical outcome. We have counted the bacteria in whole blood, buffy coats, lysed buffy coats, and bone marrow aspirates from culture positive enteric fever patients using the pour plate method. The median number of bacteria in whole blood from 375 patients was lcfu/ml (IQ range<0.3-5). In 29% of patients there was lcfu/5mls blood and so 13mls of blood is required for a 95% culture positive rate in S. typhi infections. In 187/375, 100 μl comprising the buffy coat layer, was separated from I ml of whole blood. 37.5% (95% Cl 32.9-42.1) of the total bacteria were concentrated in this layer. In 81/375 patients for the median numbers of bacteria per infected cell were found, by digitonin lysis of buffy coats, to be 1.3 cfu per cell. In the bone marrow of 78 patients there were an averange of four times as many bacteria as from the blood of the same patients for equal volumes. There was a negative, significant correlation (p<0.005) between counts and age, and duration of fever preceeding hospital admission. There was a positive significant correlation (p=0.05) between counts and temperature, fever clearance time after treatment, and multi-drug resistance of the bacterial isolate, despite similar pretreatment histories. In summary if blood culture is used to establish a diagnosis at least 13mls must be cultured. The S. typhi is concentrated in the buffy coat layer which provides a reliable specimen for the isolation of S. typhi. Bone marrow is the best specimen from which to reliably culture of S. typhi. Multidrug resistant S. typhi is present in higher numbers in the blood than is found with fully sensitive strains. There is a direct correlation between bacterial load and clinical response to treatment.