Evaluation of direct tube coagulase test in diagnosing staphylococcal bacteremia

Blood Stream Infections (BSIs) are one of the most common nosocomial infections encountered in a hospital. It occurs 2 to 7 times more often in ICU patients than in ward patients and is associated with high rates of mortality and morbidity. Staphylococci is the most commonly encountered blood culture isolates for which, rapid and reliable methods for detection are warranted.

To study the efficiency of direct tube coagulase test (DTC) in comparison with slide/tube coagulase test for early detection of Staphylococcal bacteraemia.

This was a prospective study conducted in a tertiary care hospital, between January 2009 to December 2009. Two sets of blood cultures were obtained from each patient with a suspicion of Staphylococcal bacteremia. Both, direct tube coagulase test and conventional biochemical tests were done on the samples, to identify the species.

Cohen's kappa coefficient of agreement was used to detect the differences between the two modes of detection.

Ninety four samples (out of 460) yielded the growth of Gram positive cocci in clusters. The commonest isolates were Staphylococcus aureus (42.5%), Staphylococcus epidermidis (36.2%), Staphylococcus haemolyticus (8.6%), Staphylococcus cohnii (4.3%). Cohen's kappa coefficient which implies the extent of agreement of the results between the Direct Tube Coagulase test and conventional methods, was 95.6% along with sensitivity of 95.5% and specificity of 100%.

Direct Tube Coagulase test (DTC) can be used for early detection of Staphylococcal bacteremia. It shows an almost perfect agreement with conventional coagulase test.