[The significance of blood culture contamination in microbiological laboratories]

Blood cultures in open systems are exposed to an additional danger of contamination, when manifold subcultures are made. The blood tests of 48 patients with suspicion to sepsis were investigated in two parallel series with 6 cultures each. The blood culture flasks of one series were for the first time opened to subculture on the 10th day, those of the second series on the 3rd, 6th and 10th day. The contamination rate which was to be led back to laboratory work was in the first series nearly 1.1% (total contamination rate 2.8%), in the second series nearly 14% (and 15.8%, respectively). For blood cultures closed systems are to be recommended. If with open systems is worked, a subcultivation is to be recommended only after macroscopically visible growth or only on the 10th day.