An outbreak is usually defined as either two or more linked cases, or an increase in cases against the normal background levels of an organism (Anonymous, 2011)! When the background level of an organism is zero, one case can and should be recognised as an outbreak (Anonymous 2012). The normal background level of nosocomial bloodborne viruses (BBV) should be zero, and consequently, a single nosocomial BBV transmission should be considered an outbreak. This Outbreak Column is focused on recent nosocomial BBV outbreak reports. This is not so much to emphasise that they should be classified as 'infection control never events', but rather because the fact these relatively small sporadic outbreaks occur, suggests that standard infection control precautions may not be practised sufficiently well generally to prevent BBV outbreaks. Included in this column are nosocomial BBV outbreak investigations implicating re-used cotton wool balls, colo-noscopy procedures, lancing devices and details of one outbreak that occurred in two hospitals. There is a good degree of variation in the depth of the investigations and in the certainty with which the investigators present their case for the probable causative transmission pathways. This is in the main due to the retrospective nature of outbreak investigations. This Outbreak Column will not include detailed discussions of phylogenetic analysis presented in the papers - this is beyond my expertise. It is assumed that the authors and the journals' peer reviewers have accepted that the evidence presented is sufficient to justify a diagnosis of nosocomial BBV cross-transmission.
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