Editor—In a recent study by Jawaheer et al, the relation between volume of blood cultured and detection rate of coagulase negative staphylococci (CNS) was studied in neonates.1Blood culture bottles inoculated with small blood volumes yielded positive results more frequently than those seeded with larger volumes: 14 of 29 (48%) bottles inoculated with less than 0.5 ml were positive; only seven of 44 (16%) containing ⩾0.5 ml of blood grew the organism (P=0.006). These results are quite unexpected, because large blood volumes should have contained higher number of circulating organisms and, therefore, the positive rate of these bottles should have been higher, but no explanation for this apparent paradox was suggested by the authors.

The overall positivity rate found in the study, and particularly that of the low blood culture bottles, is substantially higher than that found in most blood culture studies, but lack of clinical or laboratory data on the culture positive patients makes it impossible to distinguish contamination of blood cultures from true bacteraemia. This distinction is very important …