The Where is Norovirus Control Lost (WINCL) study: an enhanced surveillance project to identify norovirus index cases in care settings in the UK and Ireland

Background: Norovirus outbreaks have a significant impact on all care settings; little is known about the index cases from whom these outbreaks initiate.

Aim: To identify and categorise norovirus outbreak index cases in care settings.

Methods: A mixed-methods, multi-centre, prospective, enhanced surveillance study identified and categorised index cases in acute and non-acute care settings.

Results: From 54 participating centres, 537 outbreaks were reported (November 2013 to April 2014): 383 (71.3 in acute care facilities (ACF); 115 (21.4 in residential or care homes (RCH) and 39 (7.3 in other care settings (OCS). Index cases were identified in 424 (79 outbreaks. Of the 245 index cases who were asymptomatic on admission and not transferred within/into the care setting, 123 (50 had been an inpatient/resident for 4 days. Four themes emerged: missing the diagnosis, care service under pressure, delay in outbreak control measures and patient/resident location and proximity.

Conclusion: The true index case is commonly not identified as the cause of a norovirus outbreak with at least 50% of index cases being misclassified. Unrecognised norovirus cross-transmission occurs frequently suggesting that either Standard Infection Control Precautions (SICPs) are being insufficiently well applied, and or SICPs are themselves are insufficient to prevent outbreaks.