How long is norovirus (norovirus) contagious?

How Long is Norovirus Contagious?

Infected individuals should be considered contagious during their acute illness and for 48-72 hours after symptom resolution, based on CDC infection control guidelines. 1

Peak Contagious Period

The most infectious period occurs during two distinct phases:

• Acute illness phase: When symptoms are active, with peak viral shedding occurring 2-5 days after infection, reaching approximately 100 billion viral copies per gram of feces 1
• Early recovery phase: The 24-72 hours immediately following symptom resolution, when individuals continue shedding virus at high levels 1

Practical Isolation Recommendations

Healthcare and Food Service Workers

Healthcare staff and food handlers must be excluded from work during their illness and for 48-72 hours following complete symptom resolution. 1, 2

Institutional Settings

• Patients in healthcare facilities: Should remain isolated during illness and for 24-48 hours after symptoms resolve 1, 2
• Cruise ship passengers: Should voluntarily isolate in cabins during illness and for 24-48 hours post-recovery 1
• Long-term care residents: Require isolation during illness and 24-48 hours after symptom resolution 2, 3

Exposed but Asymptomatic Individuals

In healthcare settings, exposed staff and patients should not transfer to unaffected areas for typically 48 hours after exposure to minimize spread from incubating infections 1, 2

Important Caveats About Viral Shedding

While norovirus can be detected in stool for an average of 4 weeks following infection, this prolonged detection does not necessarily indicate ongoing contagiousness. 1, 3 The critical distinction is that:

• Peak infectivity occurs during acute illness and the first 24-72 hours post-recovery 1
• Whether virus detected beyond this period represents infectious particles remains unknown due to inability to culture human norovirus 1
• Negative stool testing is NOT required before returning to work or normal activities 1, 2

Asymptomatic Transmission Risk

Up to 30% of norovirus infections are asymptomatic, and these individuals can shed virus, though at lower levels than symptomatic persons 1. The role of asymptomatic infection in transmission remains unclear, but asymptomatic food service workers who test positive during outbreak investigations should still be excluded or restricted 1

Historical Context

An older CDC guideline from 1990 noted that infectivity can last for as long as 2 days after symptom resolution 1, which aligns with the current 48-72 hour post-symptom exclusion recommendations in the more recent 2011 guidelines 1, 2

Infection Control During Contagious Period

During the contagious period, strict measures are essential:

• Hand hygiene: Wash with soap and running water for at least 20 seconds; alcohol-based sanitizers are insufficient as substitutes 1, 2, 3
• Environmental disinfection: Use chlorine bleach solution (1,000-5,000 ppm) on contaminated surfaces, particularly bathrooms and high-touch areas 2, 3
• No bare-hand contact with ready-to-eat foods 1, 2