Clot culture in typhoid fever.

In early diagnosis of typhoid fever, the emphasis has for long been on the isolation of S. typhi from blood culture. Clot culture techniques have not enjoyed the same vogue, although they are largely used in areas where the disease is endemic. Felix (1924) found that clot culture was hardly ever unsuccessful if blood culture was successful, but that the reverse was frequently true. He attributed this to the removal of any bactericidal serum factors before culturing the clot. In an earlier publication (Thomas, Watson, and Hewstone, 1954) we recommended the use of streptokinase bile broth (containing 100 units/ml. of streptokinase) as a culture medium for blood clot. Our experience with this method since then has amply borne out the initial favourable results, and as a result of its application it soon became apparent that the results of clot culture were considerably better than those of blood culture. Thus, in a series of 48 cases where both clot culture and blood culture were performed before the introduction of streptokinase and one or both yielded a positive isolation, there were 38 positive blood cultures and 36 positive clot cultures. In a further series of 99 cases since the introduction of streptokinase there were 48 positive blood cultures and 93 positive clot cultures, an increase of 45 in favour of the latter. Two possibilities arose that might be responsible for these results: (1) streptokinase might exert a specific stimulating effect on the growth of S. typhi, or (2) removal of the serum before culturing the clot increases the chances of obtaining a positive isolation. We have investigated (1) at some length, but have been unable to demonstrate any specific effect on growth, and the action of streptokinase appears to be, as we previously reported, purely an enzyme one concerned with fibrinolysis. A study was therefore undertaken of the effect of serum factors on the isolation of S. typhi from blood clot and whole blood. Serum Factors in Clot Culture