Norovirus Spikes in Bay Area Wastewater Amid Nationwide Rise in Outbreaks

Norovirus levels in Bay Area wastewater are spiking as cases of the highly contagious stomach bug are on the rise this month, according to a Stanford-based monitoring system and data from the Centers for Disease Control and Prevention.

During the week of Dec. 5, the most recent data available from the CDC, state health departments nationwide reported 91 new outbreaks — a 31% increase since the last reporting period a week earlier. It’s the highest number recorded for that week since 2012, topping the previous high mark of 65.

The virus, commonly known as the stomach flu, infects approximately 19 million to 21 million people in the U.S. each year, according to the CDC, and accounts for about 50% of all foodborne disease outbreaks. It can cause diarrhea, stomach pain, vomiting and nausea.

In the Bay Area, the national rise coincides with spiking levels of norovirus in wastewater for some communities. Of the four sites that are tested for norovirus in the region, samples from three found that the virus levels have increased in wastewater.

Samples from WastewaterSCAN, a Stanford-based program that monitors diseases in local wastewater systems, show that norovirus levels in wastewater in San José, Palo Alto and Santa Cruz have recorded some of the highest levels in nearly two years.

Santa Cruz’s samples, which come from the city’s wastewater treatment facility, reported the largest increase among the three since the beginning of October.

Since then, an elementary school closed following more than 90 cases of the virus, prompting a public health alert from the county. The number of cases later jumped to more than 210 countywide since mid-October, according to the county’s Health Services Agency.

Samples from wastewater facilities in San Francisco, San Rafael and Redwood City also showed elevated levels of the virus as recently as Dec. 29.

The virus is most likely to result in outbreaks between the months of November and April, according to the CDC, and is spread through close contact with sick people and contaminated food, water and surfaces.

Once infected, those who get sick typically recover in three days. However, the virus can still require medical care and is very rarely fatal for some, especially children under the age of 5 and adults 85 years or older. It causes an average of 900 deaths a year in the U.S.

To prevent the spread of the virus, the CDC recommends washing hands with soap and water for at least 20 seconds, especially after using the bathroom and before eating or handling food. Hand sanitizer does not work against norovirus, according to the CDC, and shouldn’t be used in place of handwashing.

Other recommendations include: washing laundry well with hot water, regularly sanitizing kitchen surfaces and utensils, washing fruits and vegetables, and thoroughly cooking shellfish and oysters.