What it is:

• Norovirus is a name for a group of viruses in the Caliciviridae family. They are named after the original strain, the Norwalk virus, which was discovered during an outbreak of the disease caused by the virus at an elementary school in Norwalk, OH, in 1968.
• Diameter of norovirus: between 0.027 and 0.032 micron.
• Viruses are parasitic microbes, about 100 times smaller than bacteria.

Where found:

• Spread through poor toilet hygiene, drinking infected water or eating infected food, through contact with infected people or surfaces.
• Outbreaks:
• Occur worldwide. Different strains of this category of viruses are named for the location in which they were first identified.
• Often associated with septic, sewer or fecal contamination of private wells, small water systems, community water systems, recreational waters, pools. Cross-connection of sewage and drinking water systems is a cause.
• Washing food with contaminated water is a cause, as is eating shellfish (raw or steamed) from polluted waters. Contaminated salad ingredients are often a cause.

Health effects:

• Causes a form of gastroenteritis sometimes called “winter vomiting disease” or “stomach flu.” A common disease, but usually not fatal, with no long-term effects. Vulnerable people (children, elderly, immuno-compromised) may require medical attention.
• Symptoms typically occur between 24 and 48 hours after exposure, last 24-60 hours, and include nausea, vomiting, diarrhea, abdominal pain, muscle aches, headache, fatigue and low-grade fever.
• Hydration is an important recovery aid.

Regulation:
The US Environmental Protection Agency (EPA) requires:

• For public surface water supplies: Minimum of 4-log (99.99 percent) removal/inactivation (applies to all enteric viruses).
• For public groundwater supplies (all viruses): Sanitary surveys of EPA-defined community and non-community water systems, as well as monitoring of source water of groundwater systems not required to remove/inactivate to 4-log level. Monitoring triggered by positive total coliform sample in distribution system.

Water treatment:

• A variety of disinfection methods may be effective, including chemical oxidation, ultraviolet, distillation, etc. Note that noroviruses have survived in water with up to 10 parts per million (ppm) chlorine, well above public drinking water levels.
• Finer filtration methods: reverse osmosis, nanofiltration and some ultrafiltration systems.