[When should a stool culture be done in adults with nosocomial diarrhea?]

To assess the diagnostic efficacy, cost and possible corrective measure of the indications for routine stool cultures in nosocomial diarrhoea in adults.

A retrospective study over a 10-month period of 660 standard stool cultures, 256 of which were conducted after the 3rd day of hospitalisation, conducted in 528 patients at the hospital centre in Pau.

The positivity rate of the stool cultures was of 26/336 patients (7.7%), and of 37/404 examinations (9%) within the first three days of hospitalisation, versus 2/192 patients (1%) and 3/256 examinations (1%) after the 3rd day of hospitalisation (p<0.05). In 83 patients a stool culture was repeated, and was only positive in one patient with an initially negative culture. If a stool culture had not been performed after the 3rd day, 2 infections would not have been diagnosed (1 salmonella and 1 K. oxytoca) and 256 stool cultures could have been economised (estimated cost: 6,144 euro). Moreover, by eliminating repeated stool cultures, 3 infections would not have been diagnosed (2 salmonella, and 1 K. oxytoca) and 321 stool cultures would have been avoided (estimated cost: 7,704 euro). If the stool cultures had been conducted after the 3rd day of hospitalisation only in those aged over 64 with comorbidity, immunosuppression or within the context of an epidemic, no false negative would have been observed and 149 stool cultures would have been economised (estimated cost: 3,576 euro). The positivity rate of the search for C. difficile, only conducted on explicit request from the practitioners, was of 5/23 (22%) and 4/28 (14%) before and after the 3rd day of hospitalisation (non-significant difference).

Restriction of standard stool cultures after the 3rd day of hospitalisation to patients aged over 64 with comorbidity, to the immunodepressed, and within an epidemic context would economise around 4,300 euro per month in a medium-sized general hospital. No systematic restriction should be applied to the search for C. difficile.