Responding to Norovirus: How Laboratories Can Improve Diagnostics and Readiness

As the 2025–2026 winter season unfolds, norovirus, commonly referred to as the “winter vomiting disease” has reemerged. Cases are rising earlier than expected, emphasizing that this highly contagious virus remains a major public health concern, and increased patient influx is overwhelming urgent care centers and physician offices. 

While the CDC data suggests that current uptick is lower than last year’s, public health experts continue to underscore that robust surveillance, early detection, and strengthened infection prevention and control strategies are paramount in containing transmission before isolated cases become outbreaks. 

This article provides an overview of norovirus surges in recent years and explores what it means for clinical laboratories’ readiness, diagnostic strategies, and public health preparedness.

What is norovirus and how does it spread?

Noroviruses (commonly called “winter vomiting disease” or “stomach flu”) belong to the Caliciviridae family and are single-stranded RNA viruses that remain the leading cause of acute gastroenteritis globally. 

First identified during a 1968 gastroenteritis outbreak in Norwalk, Ohio, the virus was initially referred to as “Norwalk virus.” Norovirus is highly contagious and spreads rapidly through direct contact with infected individuals, contaminated surfaces, water, and food sources. 

Typical symptoms of a norovirus infection include sudden onset of nausea, vomiting, diarrhea, and stomach cramps, often accompanied by low-grade fever or body aches. The characteristic symptom of abrupt onset of vomiting combined with diarrhea (and the fact that most infections occur in the winter) is what earned norovirus its well-known moniker the “winter vomiting disease.”

Norovirus is most contagious during the first days of infection, especially when a person has active symptoms like vomiting. However, research shows that people can continue to spread norovirus for two weeks or longer after symptoms resolve. 

Why is it important to test for noroviruses?

Testing for norovirus is essential for 5 key reasons:

1. Highly contagious nature of norovirus

Norovirus is highly contagious, with its basic reproduction number (R₀)—a measure of how many people one infected person is likely to infect—ranging from 1.1 to as high as 7.0, depending on the setting. 

The highest transmission rates occur in congregate settings, nursing homes, and long-term care facilities. The virus's short incubation period (with symptoms appearing within one to two days of exposure), its ability to spread through multiple routes, and its high environmental resilience make it extremely difficult to control without early detection and timely prevention measures.

2. Nonspecific clinical symptoms 

Norovirus causes symptoms that look like many other stomach infections, making it difficult to diagnose without testing. Laboratory confirmatory testing is needed to differentiate viral from bacterial infections, helping guide appropriate treatment and management decisions, avoid unnecessary antibiotic use, and support antimicrobial stewardship. 

In high-volume, urgent care settings, rapid identification is essential to prevent isolated cases from progressing to outbreaks. Early detection enables rapid implementation of infection prevention and control (IPC) measures, such as patient cohorting, enhanced sanitizing and sterilizing, and other outbreak management strategies. These measures are especially critical in high‑risk settings like hospitals and long‑term care facilities.

3. High healthcare and economic burden 

Norovirus carries a high healthcare and economic burden, resulting in millions of cases and billions of dollars in medical and healthcare costs. A 2020 study estimated norovirus burden in the US at approximately $10.6 billion annually, making it one of the most expensive causes of acute gastroenteritis. 

The transmission is more frequent in close-contact settings, especially in healthcare facilities, which explains why more than 60 percent of all reported norovirus outbreaks in the US are linked to hospital-acquired infections. 

On a global scale, norovirus causes an estimated 200,000 deaths annually. Altogether, norovirus is estimated to pose an annual global economic burden of nearly US$60 billion, underscoring its significant public health and economic impact. 

4. Data-driven decision-making 

Data-driven decision-making and surveillance rely on accurate laboratory testing and reporting and monitoring of infection positivity. Analyzing lab-confirmed cases can help identify and predict emerging trends, detect new strains, and improve outbreak preparedness.

5. Increasing awareness of norovirus

Increasing awareness of norovirus among clinicians, laboratorians, and public health officials is paramount to improving diagnostics and IPC measures. Although norovirus outbreaks sometimes capture media and public attention, the virus’s broader health and economic impact is often underestimated, in part because infections are often perceived as self-limiting and short lived. Improving awareness of norovirus’s healthcare and economic impact can better inform decisions on prevention and control strategies, especially around the seasonal outbreaks.

What is driving norovirus resurgence?

Seasonality of norovirus 

In the US, norovirus follows a seasonal pattern, peaking in winter months and causing most outbreaks from November through April. While the CDC estimates that approximately 2,500 norovirus outbreaks occur annually in the US, CDC NoroStat data report 447 norovirus outbreaks between August 1, 2025, and January 8, 2026, a 50 percent decrease compared with last year. 

However, what is concerning is the timing of norovirus activity. Similar to last year, the 2025–2026 season is showing earlier-than-expected norovirus activity, with trends in outbreak occurrences and rising norovirus-related cases indicating a spike ahead of the traditional winter peak. This early seasonal onset can prolong transmission duration, increase exposure during travel and indoor gatherings, place additional strain on healthcare systems, and increase the risk of isolated cases escalating into larger outbreaks before detection and control measures can be implemented.

New norovirus strains 

Historically, the GII.4 variant has predominated globally from the early 2000s, driving most seasonal norovirus outbreaks. More recently, emerging variants such as GII.17 have gained prominence, reflecting ongoing viral evolution and changing population susceptibility. During the 2024–2025 season, GII.17 accounted for a substantial 75.4 percent of reported outbreaks, while the proportion of GII.4 outbreaks declined to 10.7 percent. This shift in circulating strains likely contributed to the earlier-than-expected surge, as a large portion of the population had limited prior exposure and immunity to GII.17, making them more susceptible to infection.

Post-pandemic immunity “debt” 

During the COVID-19 pandemic, widespread non-pharmaceutical intervention (NPIs) measures such as masks, social distancing, and lockdowns significantly reduced exposure to common pathogens, and hampered their circulation pattern, including norovirus. This lack of exposure possibly led to lower natural immunity across all age groups creating an “immunity debt.” As pandemic-related restrictions are lifted, the “less-immune” population is now susceptible to norovirus outbreaks caused by new and evolving norovirus strains.

Behavioral and environmental factors 

As pandemic restrictions have eased, social interactions, holiday gatherings, public events have returned to, or even surpassed, pre-pandemic levels. Combined with norovirus’s extreme contagiousness, low infectious dose, and environmental impact, these factors facilitate increased transmission. 

What is the current landscape of norovirus testing?

Historically, norovirus detection relied on epidemiological criteria, i.e., the presence of symptoms and a lack of bacterial pathogens in the stool culture. Techniques like electron microscopy and ELISA for antigen detection have also been used. However, due to their low to moderate sensitivity and associated risk of misdiagnosis, these modalities are not recommended for sporadic gastroenteritis cases and during outbreaks. 

The current gold standard for norovirus detection is real-time PCR, either as an individual assay or as part of multiplexed syndromic gastrointestinal (GI) panels. The high sensitivity and specificity of PCR allows for the detection of very low viral loads and can also facilitate the genotyping of the virus present in the patient sample.

How can laboratories prepare for seasonal norovirus surges?

Planning for capacity

Seasonal norovirus surges, especially outbreaks, can result in drastic increase in sample volumes placing a substantial strain on lab workflows, instruments, and personnel capacity. 

Laboratories should regularly review historical lab data and current surveillance trends to build predictive models  that forecast demand and support staffing and device planning.  Cross-training lab personnel to handle intra/interdepartmental functions, implementing flexible schedules models, and identifying surge personnel can help prevent bottlenecks. 

During surge periods, laboratories must maintain effective supply chain management and ensure adequate inventories of reagents, assay kits, standardized collection media, etc. Laboratories should also establish contingency plans for any unexpected shortages, including alternative vendors and emergency stockpile inventory to ensure undisrupted testing during peak periods. 

Ensuring test performance and robustness

Validating tests under high-volume conditions is essential to ensure assay performance, accuracy, and turnaround times consistency during seasonal surges. During this time, labs should also maintain backup instruments and plan alternative workflows to reduce downtime and preserve testing continuity in the event of instrumental or staffing issues. 

Establishing effective quality controls 

Incorporating effective (if needed, additional) quality control checks in the unidirectional workflow can help evaluate performance inconsistencies early, which in turn will reduce the risk of reporting errors when high-demand situations.

Data reporting and monitoring

Building and monitoring test dashboards can help track not only test positivity trends but also volume and assay performance metrics, which further enables timely reporting to state health departments and public health authorities for timely intervention. 

Enhancing client engagement 

During outbreaks, laboratories should proactively educate clinicians on appropriate testing indications, test utilization best practices, and expected turnaround times to support efficient clinical decision-making. Establishing effective multi-channel and omni-channel communications strategies (e.g., client bulletins, tech notes, recent positivity trends, automated alerts, etc.) allows laboratories to promptly inform clients of unexpected increases in positivity or any suspected outbreaks.

Initiating public-private partnership 

Although individual norovirus cases are not reported, healthcare providers must report outbreaks to the local/state health agencies, which are encouraged to report the same to the CDC. This may be resulting in the under-reporting of norovirus cases in the US. This gap in the reporting system highlights the need for greater collaboration between labs, clinicians, and public health agencies to strengthen outbreak surveillance and response strategies.

Collaboration strengthens outbreak response 

Norovirus infections pose a substantial public health burden, both in the US and globally. Rapid, reliable, and robust laboratory preparedness and diagnosis of norovirus are crucial, along with close collaboration among healthcare providers, laboratories, and public health agencies to support data sharing, expedited test development, and effective outbreak management. As norovirus circulation patterns continue to evolve post-pandemic, clinical laboratories play a central role not only in diagnosing infections but also in guiding timely IPC and public health response.