Laboratory and clinical investigation of recovery of Salmonella typhi from blood.

An experimental study was undertaken of isolation of Salmonella typhi from artificially infected whole blood and blood clot prepared either with small numbers of freshly isolated strains or with the S. typhi Ty2 strain. Results showed that 8 ml of whole blood required a minimum of 50 ml of bile salt broth to dilute the bactericidal effect of the serum. However, the isolation rate for recovery in 210 cases of enteric fever was only 64% when 50 ml of medium was used, as compared to 92% recovery from blood clot from the same group incubated in streptokinase bile salt broth. This probably reflects a very low grade bacteremia in many of the patients. Further investigation showed that, ideally, between 150 and 200 ml of medium is required for satisfactory whole-blood culture. Both the experimental study of artificially infected clots and recovery rates from patients indicate that rapid clot dissolution with streptokinase is preferable to whole-blood culture; this experience has been amply confirmed by almost 5,000 cases over a 20-year period. A 15-ml volume of bile salt broth with 100 U of streptokinase is adequate for the clot from 8 ml of blood, and savings on media and incubator space have considerable cost benefits in developing countries.