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Norovirus-infected patients at LTC facilities shed virus for 3 weeks
Nearly half of elderly patients infected with norovirus during outbreaks at long-term care facilities asymptomatically shed the virus at high levels for at least 3 weeks, according to recent data.
The findings suggested that some individuals can clear infection quicker than others, according to researcher Veronica P. Costantini, PhD, from the CDC’s division of viral diseases, and colleagues.
In the prospective study, the researchers investigated norovirus outbreaks at 43 long-term care (LTC) facilities in Oregon from November 2009 to January 2013. Ten naturally occurring norovirus outbreaks were evaluated for epidemiology, virology and genetic host characteristics. All outbreaks selected for analysis were reported to local health departments within 3 days of onset of the first case, involved at least 10 symptomatic patients, had 20 possibly exposed patients and were ongoing at the time of notification.
The researchers categorized LTC facility participants as cases (n = 62), exposed controls (n = 34) or nonexposed controls (n = 18), based on symptomatology and interaction with an infected person.
Saliva samples were collected from cases and exposed controls and tested for histo-blood group antigens (secretor, ABO and Lewis type). Stool specimens from cases and exposed controls were tested for norovirus infection using qualitative PCR, or confirmed infection through fourfold increase in serum antibody titers.
More than 100 stool samples were collected from case patients, 55 of which were acute, 49 were convalescent and 47 were acute/convalescent pairs. In addition, 59 samples were collected from exposed controls; 29 were acute, 30 were convalescent, and 26 were acute/convalescent pairs. Among the 179 samples, norovirus was detected in 46% of acute cases, 27% of convalescent cases and 11% of control stool samples. Prolonged virus shedding (at least 21 days’ duration) occurred in 47% of the 35 cases with a positive acute stool sample.
“Whether the shedding of viruses after 3 weeks represents infectious virus is a key question that will need to be answered,” Costantini and colleagues wrote.
The researchers also identified several GII.4 genotypes including Den Haag (n = 3), New Orleans (n = 4) and Sydney (n = 2), as well as genotype GI.1 (n = 1). Compared with other genotypes, GII.4 Sydney had significantly higher viral load, with cases and controls shedding comparable amounts of virus.
“An interesting observation in our study was the fact that although individual virus loads were similar or higher (range, 10⁵-10¹³ genomic copies/g of stool) than noted in previous reports, the highest viral loads correlated with the recent emergence of new GII.5 variants,” Costantini and colleagues wrote. “Because outbreaks with higher viral load occurred relatively soon after the emergence of GII.4 New Orleans in 2009 and GII.4 Sydney in 2012, increased viral load in both symptomatic and asymptomatic individuals may suggest more efficient virus replication.” – by Jen Byrne
Disclosure: Costantini reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.