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Study Finds Food and Healthcare Workers More Susceptible to Norovirus

Individuals who handle foods in the course of their work, as well as those working in healthcare settings, have a higher risk for infection with highly contagious, gastroenteritis-inducing noroviruses when an outbreak occurs where they work; with asymptomatic infections observed more frequently in those who handle foods, according to the results of a study published recently in the Journal of Clinical Virology1.
Although gastroenteritis is often the result of bacterial infections, the human norovirus (NoV) has been identified as one of the main causes of global acute non-bacterial cases.2 Several studies have now confirmed the important roles played by asymptomatic and symptomatic food handlers (FHs) and healthcare workers (HCWs) in causing or spreading NoV both in foodborne outbreaks and person-to-person transmitted outbreaks.3 To date, however, there have been no studies assessing the risk to FHs and HCWs of acquiring NoV during outbreaks in their workplaces. A recently published study aimed to assess this level of risk.1
The study was presented by first author Aurora Sabrià from the Enteric Virus Group in the Department of Microbiology and the Nutrition and Food Safety Research Institute at the University of Barcelona in Santa Coloma de Gramanet, Spain, and her colleagues. The stated objectives of the study were "... to analyze the occurrence of NoV infections among FHs and HCWs in outbreak settings. Percentages of subjects who were symptomatically or asymptomatically infected were determined for different types of outbreaks and concentrations of NoV shedding were analyzed in correlation with symptoms. Finally, sequence analysis was applied to confirm linkage between cases and asymptomatic individuals."
To accomplish their stated goals, Sabrià et al screened fecal samples from a total of 242 FHs (cooks, kitchen assistants, waiters, and dining room instructors and assistants) and HCWs (caregivers, entertainers, instructors, and additional staff members) during 59 previously reported outbreaks in Spain caused by NoV,4 as well as eight outbreaks unrelated to NoV.
The results of the study indicated that almost six of every ten worker sampled (59.1%) screened positive for NoV. Of these individuals, 70.6% were asymptomatic, which is particularly troubling, as they would likely have been unaware of their NoV status and related ability to infect others. As compared with the total study population, differing percentages of NoV positive status were detected between FHs (60.4%) and HCWs (46.3%). Furthermore, a relatively large difference was detected in the percentages of asymptomatic status between FHs (47.0%) and HCWs (13.0%). This difference was likely due to significantly more frequent asymptomatic infections among those working in restaurants and hotels as compared to nursing homes and healthcare institutions. Additionally, the mean viral load levels detected for symptomatic and asymptomatic workers were very similar (7.51 ± 1.80 and 6.49 ± 1.93 log10 genome copies/g, respectively), again suggesting that those without noticeable symptoms were just as likely to be highly contagious. "In summary, our data highlight that infected employees may be a potential source of secondary NoV transmission," Sabrià et al said.
Regarding the broader implications of the study’s results, Sabrià et al stated that, "Since FHs are more likely to be asymptomatically infected and the amount of viruses shed in feces are as high as those shed by symptomatic ones, the risk of transmission may be higher in settings where FHs are involved. Given the importance of food handling in the transmission of NoV infections, FHs should be advised to take special care to follow good kitchen hygiene practices." The study authors also recommended that in the event of a gastroenteritis outbreak in any workplace, efforts should be made to inform employees that they have a high likelihood of becoming infected, even though they may be not be experiencing any symptoms associated with gastroenteritis. They also suggested that, "In these scenarios, hygiene practices should be reinforced among all personnel, regardless of symptoms, to reduce the risk of further spreading the illness."
William Perlman, PhD, CMPP is a former research scientist currently working as a medical/scientific content development specialist. He earned his BA in Psychology from Johns Hopkins University, his PhD in Neuroscience at UCLA, and completed three years of postdoctoral fellowship in the Neuropathology Section of the Clinical Brain Disorders Branch of the National Institute of Mental Health.
  1. Sabrià A, Pintó RM, Bosch A, et al. Norovirus shedding among food and healthcare workers exposed to the virus in outbreak settings. J Clin Virol. 2016;82:119–125.
  2. Robilotti E, Deresinski S, Pinsky BA. Norovirus. Clin Microbiol Rev. 2015;28:134–164.
  3. Belliot G, Lopman BA, Ambert-Balay K, Pothier P. The burden of norovirus gastroenteritis: an important foodborne and healthcare-related infection. Clin Microbiol Infect. 2014;20:724–730.
  4. Sabrià A, Pintó RM, Bosch A, et al. Molecular and clinical epidemiology of norovirus outbreaks in Spain during the emergence of GII.4 2012 variant. J Clin Virol. 2014;60:96–104.
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