A norovirus outbreak in a nursing home: norovirus shedding time associated with age

Norovirus (NoV) GII.4 has been identified as predominant in outbreaks in the long-term health-care facilities.

NoV excretion during an outbreak of gastroenteritis affecting 19/42 residents and 12/33 employees was investigated in a Taiwan nursing home.

Real-time reverse transcription polymerase chain reaction (RT-PCR) was used to quantify viral RNA from stool samples up to the point of negative detection.

Initial fecal viral loads in affected residents were higher than in affected employees (p=0.024). Viral reduced rate was measured as 0.66/day, with a viral half-life of 1.7 days. A mixed model indicated that time (days post-illness onset), initial virus load and resident status (as opposed to employee status) were the most important determining factors of fecal NoV concentration. According to a univariable accelerated failure time (AFT) model, strong associations existed between virus excretion duration and both age (p=0.005) and resident status (p=0.004). No associations were noted between viral excretion duration and either initial viral load or diarrhea duration. According to a multivariable AFT model, age was the only factor affecting virus excretion duration.

In conclusion, outbreaks in nursing homes may have resulted from environmental contamination, the existence of asymptomatic residents and prolonged virus shedding time in the elderly and care providers. This outbreak finished quickly because frequent cleaning of the surface was done and contact precautions were taken for prolonged viral shedding residents.