Culture media supplements may be added to cultures in order to enhance the growth of fastidious organisms. If the supplement becomes contaminated then multiple false-positive cultures can occur, giving the impression of an outbreak.
Situation:
(1) A culture media supplement is added to certain types of culture.
(2) The supplement is re-entered multiple times (multi-dose).
(3) Multiple cultures become positive for the same organism or organisms.
The investigation usually starts when:
(1) the bacteria isolated is not usually a human pathogen
(2) some patients with positive cultures do not appear to be infected
The diagnosis can be established if culture of the supposedly sterile supplement yields the same pathogen as in the positive cultures from patient samples.
It can be difficult to confirm the situation if:
(1) the contaminated supplement has been discarded
(2) the use of the supplement is not identified as a risk factor
(3) the patients with positive cultures are clinically infected
