Quantitative bacteriology of peripheral venous cannulae in neonates

In a study of 50 peripheral venous cannulae removed from neonates in the special care baby unit, quantitative and qualitative techniques for cannula culture were compared and the results correlated with detailed clinical information. High-density colonization was demonstrated on the external and internal surfaces of nine, and on the external surface alone of four, cannula tips. Internal surface colonization was always associated with heavy external surface growth. In predicting high-density colonization by quantitative methods, qualitative culture in broth was 100% sensitive and 89% specific. There was a significant association between high-density colonization of the cannula tip and hub colonization, surrounding skin colonization, longer duration of cannula insertion, and slower average infusion rate. Similar organisms were isolated more frequently from the cannula tip and the hub than from the cannula tip and surrounding skin. These findings indicate that peripheral venous cannulae are a potential source of infection in neonates, that there is no advantage of techniques that identify internal surface colonization, and that most cannula tip infections have their origin in a colonized hub.