Norovirus Outbreak on an Inpatient Behavioral Health Unit
A 24-bed inpatient behavioral health unit reports five patients and three staff members with acute vomiting and watery diarrhea over 42 hours. The first patient developed symptoms 12 hours after returning from a weekend pass. The unit has two shared bathrooms, communal dining, and a group therapy room. Admissions have continued, and two nurses from a medical unit floated to the floor yesterday. Environmental services cleans the unit once daily with a quaternary ammonium disinfectant. Alcohol-based hand rub dispensers are mounted at every doorway. One patient has chronic Clostridioides difficile colonization and is currently asymptomatic. Stool specimens from two patients are pending. No staff have been excluded yet. The unit medical director asks whether the unit should be closed to admissions and what the infection preventionist recommends.
1. Construct a working case definition and calculate attack rates for patients and staff. What do the rates tell you about the likely source and the need for further investigation?
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A useful working case definition is: any patient or staff member on the unit with vomiting or watery diarrhea, with onset between the index patient's return and the current time, plus anyone with an epidemiologically linked illness who has not yet been tested. Use a broad clinical definition initially because norovirus is highly transmissible and early cases may be mild. Patient attack rate is 5 of 24, or 20.8%; staff attack rate is 3 of 38, or 7.9%, if the unit has 38 staff. The higher patient rate is consistent with shared bathrooms, communal dining, and group activities, which create repeated common exposures. The staff rate shows healthcare workers are also part of the transmission chain and may carry the virus between patients. Rates alone do not prove a food or water source, so ask about a shared meal, a contaminated bathroom, and the index patient's activities during the pass. Calculate rates by subgroup, such as patients who ate in the dining room versus those who did not, to identify a common exposure. Continue case finding because mild cases are easily missed.
2. What control measures should be implemented, in what order, and should the unit be closed to admissions?
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Institute contact precautions for all symptomatic patients and cohort them if single rooms are unavailable. Stop communal dining and group therapy, and serve meals on the unit with disposable or dedicated equipment. Change hand hygiene practice: alcohol-based hand rub is not reliable against norovirus, so staff and patients should use soap and water after contact with patients, bathrooms, and contaminated surfaces. Clean and disinfect bathrooms and high-touch surfaces at least twice daily and immediately after visible contamination, using a chlorine-based product effective against norovirus or another product with the appropriate label claim; quaternary ammonium alone may not be adequate. Exclude ill staff from work until 48 hours after symptoms resolve. Close the unit to new admissions until there have been no new cases for at least 48 hours, because admitting new patients into an affected unit exposes them unnecessarily and makes cohorting harder. The medical director should be told that closure is a control measure, not a judgment that care is unsafe. Notify public health and the hospital incident command, and track staff who floated to other units.
3. What laboratory and reporting steps are indicated, and how should return-to-work and communication be handled?
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Collect stool specimens from several early cases, not just the two already pending, and request norovirus testing by PCR; testing a few cases is enough to confirm the outbreak, and testing everyone adds little. Do not test asymptomatic patients routinely. Notify public health according to local requirements and report clusters of acute gastroenteritis, especially in a closed unit. Communicate with patients and families using plain language: what symptoms to report, why bathrooms are being cleaned more often, why communal activities are paused, and why hand washing with soap and water matters. For staff, give clear return-to-work instructions: no work until 48 hours after symptoms resolve, and strict hand hygiene after using the bathroom and before food preparation. Document who was excluded and when they may return. Advise the medical unit that received the floated nurses to watch for cases, because staff movement is a recognized amplifier in norovirus outbreaks.