Multiple outbreaks of a novel norovirus GII.4 linked to an infected post-symptomatic food handler

Abstract

Multiple norovirus outbreaks following catered events in Auckland, New Zealand, in September 2010 were linked to the same catering company and investigated. Retrospective cohort studies were undertaken with attendees of two events: 38 (24·1%) of 158 surveyed attendees developed norovirus-compatible illness. Attendees were at increased risk of illness if they had consumed food that had received manual preparation following cooking or that had been prepared within 45 h following end of symptoms in a food handler with prior gastroenteritis. All food handlers were tested for norovirus. A recombinant norovirus GII.e/GII.4 was detected in specimens from event attendees and the convalescent food handler. All catering company staff were tested; no asymptomatic norovirus carriers were detected. This investigation improved the characterization of norovirus risk from post-symptomatic food handlers by narrowing the potential source of transmission to one individual. Food handlers with gastroenteritis should be excluded from the workplace for 45 h following resolution of symptoms.

Fig. 1.

Cases of acute gastroenteritis, by date of symptom onset, in persons who attended either a medical continuing professional development event (event 1) or a trade fair event (event 2) and consumed food and/or beverage items provided by a single catering company between 20 and 22 September 2010. A case was defined as a person with an illness consisting of either vomiting or diarrhoea and one other gastroenteritis symptom.

Fig. 2.

Neighbour-joining phylogenetic analysis of the norovirus partial polymerase region B (172 bp) showing the relationship between noroviruses identified in samples from attendees at events 1–3 (▪), catering staff A, B and C (▲), environmental swab (♦) and selected reference noroviruses. Indistinguishable norovirus sequences are represented on the same node. Bootstrap values from 1000 replicates are shown where greater than 50%.

Fig. 3.

Neighbour-joining phylogenetic analysis of the norovirus P2 domain (459 bp) showing the relationship between noroviruses identified in samples from attendees at events 1–4 (▪), catering staff A, B and C (▲), selected reference norovirus GII.4 strains, and representative circulating norovirus GII.4 strains identified in New Zealand between June and December 2010. Strains are shown in the format: laboratory identity number/location/outbreak identity number/outbreak date (▼). Indistinguishable norovirus sequences are represented on the same node. Bootstrap values from 1000 replicates are shown where greater than 50%.