Norwalk Virus Infection
Contact Precautions
Norwalk virus, among a group called noroviruses, is a single-stranded RNA virus of the Caliciviridae family that causes acute gastroenteritis lasting 24 to 48 hours. Recurrent infections may occur throughout life because of the diversity of strains and the lack of long-term immunity. The virus is shed in vomitus and feces, and contamination can occur through an infected water supply, undercooked foods, or improper handwashing by an infected food preparer. Secondary transmission commonly occurs among close contacts of the infected person. Cruise ships are particularly vulnerable because of crowding and the difficulty in performing decontamination during short periods ashore.
Causes
Norwalk virus is highly contagious and transmitted via the fecal-oral route and through aerosolized particles during vomiting. The most common routes of infection include person-to-person contact and contaminated food or water supplies. Foods often involved include salad, cake frosting, clams, oysters, and meats. The virus can survive freezing as well as heating temperatures of up to 140° F (60° C). The infection causes damage to microvilli in the small intestine, producing malabsorption; vomiting occurs as a result of changes in gastric motility and delayed gastric emptying.
Complications
Complications from Norwalk virus infection include dehydration and, rarely, death. Severe dehydration can cause electrolyte abnormalities (hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis), hypovolemic shock, and cardiovascular collapse. Norwalk virus infection can exacerbate inflammatory bowel disease and has also caused encephalopathy in pediatric patients.
Assessment Findings
Symptoms develop 24 to 48 hours after ingestion of contaminated food or water or contact with an infected individual. Each gastroenteritis episode is short-lived, lasting about 1 to 2 days. Signs and symptoms typically include nausea and profuse, nonbloody, nonbilious vomiting as well as watery diarrhea, abdominal cramps, headache, low-grade fever, and myalgia. Tachycardia and possibly hypotension may occur if the patient is dehydrated. Physical examination of the abdomen usually reveals the absence of tenderness and peritoneal signs.
Diagnostic Tests
Stool specimens can detect isolates for Norwalk virus, although isolated cases of infection usually don’t require laboratory testing. Stool culture will be negative for infectious bacteria and hemoglobin, and fecal leukocytes will be absent. Because studies are very costly, stool evaluation is not recommended unless strong public health indications exist.Related posts:
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