A friend was just diagnosed with norwalk virus infections, is that a serious condition?

Not usually: Norwalk-like viruses produce a non-inflammatory watery diarrhea which is generally self-limiting and from which most people recover uneventfully.

Not generally: For people in otherwise good health, and not at extremes of age, norwalk virus causes about a week of misery, with abundant nausea, vomiting, and diarrhea. It can lead to dehydration. People with underlying health conditions, taking other meds, may be at increased risk for problems; dehydration, inability to take meds, etc.

Not normally: Norwalk virus causes viral gastroenteritis often within 24 to 48 hours of exposure. Most often the symptoms last from 12 to 48 hours. Sx's may include nausea, vomiting, diarrhea, abdominal cramps, headache, muscle pain, low-grade fever & malaise. Norwalk virus occurs more often in adults & older children as compared to infants / toddlers. Need to avoid dehydration.

Agree with Dr.FH&R: Norwalk virus is self-limited, but can cause death in people with other disorders. It is highly contagious and not neutralized by alcohol based sanitizers. You need to wash you hands with soap and water. Use CDC recommended cleansers to cleanse the environment and objects.