Pseudo-outbreak of rotavirus infection in a neonatal intensive care unit

A rotavirus outbreak in a neonatal intensive care unit (NICU) may have catastrophic consequences for young infants receiving critical care. From May 13, 2011 to July 11, 2011, a significant increase in stool samples testing positive for rotavirus antigens in the NICU of a university affiliated hospital was observed. Due to lack of clinical presentations suggestive of rotavirus infection in the patients and the rarity of rotavirus infection in the NICU in the past, a pseudo-outbreak was suspected.

Infection control measures were reinforced initially. To investigate the outbreak, a prospective laboratory-based active surveillance of all infants in the NICU was conducted right after the cluster was identified. Repeated testing using a modified enzyme immunoassay (EIA) kit, rotavirus RNA polyacrylamide gel electrophoresis (PAGE), reverse transcription polymerase chain reaction (RT-PCR), and retrospective chart review methods were used to confirm the pseudo-outbreak.

Seven infants in the NICU, with or without gastrointestinal symptoms, tested positive for the rotavirus antigen using the old version of an EIA kit, which indicated a possible outbreak. Active surveillance with repeated tests for recollected stool samples using a modified EIA kit showed negative results in all 24 infants in the NICU. Seven stored stool samples from four infants, which previously tested positive for the rotavirus antigen, tested negative for rotavirus using the modified EIA kit, PAGE, and RT-PCR. Chart reviews showed no clinical difference between index cases and controls. False positivity might arise from unsatisfactory specificity of the old EIA kit. After the introduction of the modified EIA kit, no rotavirus was detected in the NICU for at least 7 months.

This cluster of patients who tested positive for the rotavirus antigen in stools was confirmed to be a pseudo-outbreak. Interpretation of the old EIA for rotavirus in an NICU setting should be done with caution until the mechanism of the false-positive reaction is elucidated.