Nosocomial coagulase negative Staphylococci bacteremia: five year prospective data collection

Coagulase-negative Staphylococcus (CoNS) species, as a group, constitute a major component of the normal microflora of the human skin and mucous membranes. Over the last 20 years, there has been an increase in the documentation of infections due to CoNS, especially with S. epidermidis species, the most common cause of nosocomial primary bloodstream infections.

To determine the frequency of CoNS isolates in blood cultures, to evaluate the meaning of this isolation (contaminant or pathogen), and to determine their epidemiologic and susceptibility patterns (oxacillin, ciprofloxacin, vancomycin, clindamycin and teicoplanin).

All strains of CoNS isolated from blood cultures collected from adults and children during 1993 to 1998, were classified as contaminant or pathogenic according to NNISS criteria (1988). Infections were classified as primary or secondary bacteremia, from clinical or surgical patients, and divided by sex and age. Susceptibility patterns were also studied in both groups.

From 1993 to 1998, 1,702 positive blood cultures were recorded. CoNS were isolated from 546 samples (32%), with 306 (56%) classified as contaminant and 240 (44%) as true bacteremia. The presence of an intravenous catheter was an important risk factor. Endocarditis (47%) ans pneumonia (32%) were the most common sites leading to secondary bacteremia.

The results confirm the increasing importance of true CoNS bacteremia and confirm their association with prosthetic valve endocarditis. We emphasize the need for care at the time of blood collection, as well as the need for care in the processing of the material, so that contamination can be reduced. This will allow a more precise description of the infections caused by coagulase-negative Staphylococcus.