NEW YORK (Reuters Health) – Patients and health care workers (HCWs) with symptomatic nosocomial norovirus (NoV) infection are much more apt to transmit the virus than asymptomatic shedders, new research suggests.
In email to Reuters Health, Dr. Faizel H. Sukhrie from the National Institute for Public Health, Center for Infectious Disease and Control, Bilthoven, the Netherlands, said: “This does not mean that those asymptomatic shedders (patients and health care workers) are not infectious. But primary interest during an outbreak should be targeted at interrupting transmission from symptomatic patients and health care workers.”
NoV is the most common cause of acute gastroenteritis worldwide. In a report online January 30 in Clinical Infectious Diseases, Dr. Sukhrie and colleagues note that few studies have looked at the contribution of asymptomatic shedders to nosocomial outbreaks, although several studies have reported a high prevalence of asymptomatic shedding. [intro]
The investigators studied the contribution of symptomatic and asymptomatic patients and HCWs to NoV transmission based on data collected during outbreaks in hospitals and nursing homes.
Five outbreaks were investigated involving 28 patients with recognized symptomatic NoV infection. Through enhanced investigation and sampling, the investigators detected an additional 65 cases; nine of these (14%) were asymptomatic patients, 37 (57%) were symptomatic HCWs and 11 (17%) were asymptomatic HCWs. They didn’t have clinical data on the remaining eight people (12%; 2 HCWs and 6 patients).
“Our study shows that notified cases in an outbreak may be the proverbial tip of the iceberg,” the investigators write.
They say their findings also “clearly suggest that symptomatic shedders are more frequently involved in transmission than asymptomatic shedders” and that asymptomatic NoV-positive HCWs “only minimally contribute to the spread of infection in an outbreak setting,” despite considerable levels of virus shedding in the stool.”
“We did not observe infections caused by asymptomatic health care workers,” Dr. Sukhrie told Reuters Health. “It is likely that infected staff can safely return to work after symptoms have disappeared. This is important for hospital hygiene departments.”
The analysis also suggests that NoV infection is substantially under diagnosed in HCWs and that these undetected infections, particularly when symptomatic, may contribute substantially to outbreaks.
“Our studies show that it is important to raise awareness that NoV is a major source for diarrhea that should not be overlooked. Therefore, to reduce nosocomial transmission of NoV, frequent testing is required in any suspicious situation, for patients and health care workers alike,” Dr. Sukhrie commented.
The researchers hope their data will contribute to the development of evidence-based strategies for prevention of spread of NoV in healthcare settings.
The study was supported by ZonMw, the Netherlands Organization for Health Research and Development. The authors have no conflicts of interest.
SOURCE:
Nosocomial Transmission of Norovirus Is Mainly Caused by Symptomatic Cases
