Incidence of Hospital Norovirus Outbreaks and Infections Using 2 Surveillance Methods in Sweden

Area of Science:

• Infectious Disease Epidemiology
• Hospital Infection Control
• Public Health Surveillance

Background:

• Norovirus (NoV) outbreaks pose a significant challenge in hospital settings, impacting patient care and resource allocation.
• Accurate surveillance is crucial for effective control and prevention of hospital-acquired infections.

Purpose of the Study:

• To compare the effectiveness of two surveillance methods: clinical reporting versus laboratory confirmation.
• To estimate the incidence of norovirus outbreaks in a large hospital setting.

Main Methods:

• A prospective observational study was conducted across 194 hospital wards over two winter seasons (2010-2012).
• Clinical surveillance relied on outbreak reports (≥2 cases within 5 days), while laboratory surveillance identified clusters of ≥2 positive NoV samples within 5 days.
• NoV outbreaks were defined by specific criteria for both methods, including laboratory confirmation.

Main Results:

• A total of 135 NoV outbreaks were identified, with laboratory surveillance detecting 43 outbreaks missed by clinical reporting alone.
• The incidence of NoV outbreaks varied by season, with rates of 1.0 and 0.5 per 1,000 admissions.
• Laboratory surveillance demonstrated higher sensitivity (86%) and comparable positive predictive value (81%) compared to clinical surveillance (68% sensitivity, 88% PPV).

Conclusions:

• Integrating laboratory surveillance significantly enhances the detection and estimation of norovirus outbreaks in hospitals.
• Laboratory surveillance provides a more comprehensive understanding of NoV epidemiology within healthcare facilities.
• The findings support the recommendation of laboratory surveillance for evaluating and improving clinical surveillance systems in hospitals.