The presence of norovirus remains at high levels in different regions of USA during May 2026, according to national environmental surveillance systems. The detection of high concentrations of norovirus in wastewater shows sustained transmission outside the traditional seasonal periodespecially affecting young children and older adults, according to official agencies. The phenomenon takes place months after the usual peak of infections, which usually occurs from November to April.

Monitoring by the program WastewaterSCAN and the Centers for Disease Control and Prevention (CDC) reveals that the areas of the northeast and midwest concentrate the highest viral activity, while the west and south report levels considered medium. Between August 2025 and May 2026, CDC’s NoroSTAT system counted 1,194 norovirus outbreaks in participating states, a figure in line with the range of previous seasons, as reported by the CDC in its public reports.

He norovirus It is the main trigger of acute gastroenteritis in the United States and usually causes vomiting, diarrhea, and abdominal pain. Health authorities emphasize that, although most cases are self-limited, the risk of complications is greater in vulnerable groups due to dehydration. Environmental monitoring in wastewater has acquired relevance to capture the community circulation of the virus, since many affected people do not go to medical systems.

Program data WastewaterSCAN and the reports of the CDC indicate that norovirus outbreaks in 2026 are concentrated in the northeast and the midwest of the country. States like California, Ohio and Wisconsin They are among those that have registered the highest number of confirmed outbreaks during the last epidemiological cycle.

Wastewater monitoring has detected pockets of viral activity in urban and suburban areas, notably the San Francisco Bay and the Los Angeles metropolitan area. The analyzes allow the levels to be classified into categories of low, medium and high concentration, which allows local authorities to adapt their health responses.

According to Amanda Bidwell, WastewaterSCAN program expert, she noted: “At the national level, norovirus remains in the HIGH category due to the high concentrations observed in the last three weeks”. Environmental surveillance is used by the CDC to complement the data that comes through the NoroSTAT system, responsible for recording institutional and community outbreaks.

He norovirus provokes acute gastroenteritiswith symptoms including vomiting, diarrhea, nausea and abdominal cramps. The pictures usually appear between 12 and 48 hours after exposure, lasting one to three days, according to the CDC. In some cases a mild fever may occur.

The main route of transmission is contact with contaminated surfaces, food or water, as well as direct contact with infected people. The virus can survive several weeks on surfaces and closed environments, which explains its rapid spread in schools, hospitals, cruise ships and other collective facilities. Even after symptoms disappear, the person may continue to shed the virus for several days.

The main risk associated with norovirus is dehydration, especially in young children, older adults and immunocompromised people. Dehydration can manifest with decreased urination, dry mouth, dizziness and fatigue, symptoms that may require medical attention in severe cases.

The Centers for Disease Control and Prevention (CDC) reported that, between August 2025 and May 2026, 1,194 sprouts of norovirus through the NoroSTAT system, a figure that corresponds to the average range of the last thirteen seasons, according to official data. The percentage of positive tests for norovirus increased from 7% to 14% in the fourth quarter of 2025.

The authorities consider that the current situation is one of surveillance, but not exceptional. A CDC spokeswoman said: “The situation is high but not out of the ordinary. No national emergency has been declared and we remain attentive to the evolution of the data”.

Constant monitoring allows us to anticipate outbreaks and guide public health actions in real time. The CDC and WastewaterSCAN recommend that the population maintain preventive measures, especially in the most vulnerable groups.

According to the CDChe norovirus is responsible for approximately 900 deaths and 109,000 hospitalizations annually in the United States, in addition to millions of medical consultations. The greatest burden of disease falls on young children and older adults, who are at greater risk of complications associated with dehydration.

The number of outbreaks varies depending on the season, but environmental surveillance allows viral circulation to be detected even outside the months of highest incidence. Data from WastewaterSCAN and NoroSTAT show that the virus remains present in different regions, which facilitates the implementation of control and prevention measures.

The main recommendations from health authorities include:

• Wash your hands frequently with soap and water.
• Disinfect commonly used surfaces, especially in kitchens and bathrooms.
• Handle and cook food with care, avoiding cross contamination.
• Avoid direct contact with people who have symptoms of gastroenteritis.
• Maintain adequate hydration, especially in children and older adults.

The virus can remain active on surfaces for long periods, so cleaning and disinfection are key to reducing transmission. There are no specific vaccines or antiviral treatments for norovirus, so prevention is the main resource.

Environmental monitoring of wastewater has established itself as a fundamental tool to detect outbreaks of infectious diseases. According to the CDC, This methodology provides a comprehensive view of community circulation, since it allows the presence of the virus to be identified even in people who do not consult medical services or undergo diagnostic tests.

Authorities use this data to anticipate trends, allocate resources and issue preventive alerts, especially in contexts of high mobility or concentration of people. The resulting information has made it possible to act proactively in the face of the sustained circulation of norovirus outside the most common season.

According to the reports of the CDC and the program WastewaterSCANa sharp increase in cases is not expected in the coming weeks, although current levels remain high in several regions. Environmental surveillance will continue as a central tool to anticipate outbreaks and guide the health response.

The authorities recommend that the population be attentive to the symptoms and consult medical personnel in case of signs of dehydration, especially in risk groups. Access to up-to-date data and information transparency will continue to be priorities to reduce the impact of norovirus on public health.