Chapter 13-9: Norovirus

TEXTBOOK PRESENTATION

Acute vomiting is usually the presenting symptom. The onset of diarrhea typically follows the vomiting. Mild abdominal cramping and low-grade fever are common. Symptoms typically resolve by 3 days.

DISEASE HIGHLIGHTS

1. Calciviruses, of which norovirus and closely related viruses such as sapovirus are the most common cause of adult viral gastroenteritis, account for about 80% of cases.

2. Most commonly occurs in winter.

3. Transmission

   1. Norovirus is easily transmissible via the fecal-oral route, airborne droplets, food, and fomites.

   2. Norovirus is the most common cause of foodborne diarrhea, and numerous outbreaks have been reported in restaurants, catered events, and cruise ships.

   3. Norovirus is very stable in the environment, resisting chlorine and alcohol disinfectants.

   4. Attack rates as high as 50% have been documented in outbreaks.

4. Incubation period is 1–2 days.

EVIDENCE-BASED DIAGNOSIS

1. In almost all cases, norovirus should be diagnosed clinically based on consistent symptoms as well as ruling out exposures or risk factors that would make diagnostic testing necessary.

2. Polymerase chain reaction (PCR) testing is available to confirm a diagnosis, but testing should be reserved for public health investigations and in patients who have reasons for diagnostic testing (see Figure 13-1).

3. PCR is available as a part of some molecular multipathogen stool panels, which are increasing in clinical use. However, testing should not be performed as most cases of norovirus can be diagnosed clinically.

TREATMENT

1. Supportive care

   1. Most patients with acute diarrhea require only supportive care. Supportive care is meant to provide rehydration and symptom relief.

   2. Rehydration

      1. Oral rehydration is generally sufficient.

      2. For patients with mild diarrhea and little volume depletion, oral fluids (eg, sports drinks, pediatric electrolyte drinks, and soup broth) are appropriate rehydration.

      3. For patients with more significant volume depletion, oral rehydration solutions should contain NaCl, KCl, HCO₃ or citrate, and glucose. The World Health Organization oral rehydration solution has the following composition:

         1. Sodium: 75 mmol/L

         2. Chloride: 65 mmol/L

         3. Glucose: 75 mmol/L

         4. Potassium: 20 mmol/L

         5. Citrate: 10 mmol/L

      4. If this solution is not available, patients can be instructed to mix the following in 1 L of water

         1. One-half teaspoon of salt

         2. One-quarter teaspoon of baking soda

         3. 8 teaspoons of sugar

      5. In patients who cannot tolerate oral rehydration or who are very volume depleted, intravenous fluids (lactated Ringer solution or normal saline) are indicated.

   3. Antidiarrheals (such as loperamide) are safe and effective for patients without bloody diarrhea (dysentery) or concern for C difficile infection. Using antidiarrheals in a patient with dysentery or C difficile may lead to:

      1. Prolonged fever

      2. Toxic megacolon and colonic perforation

      3. Hemolytic uremic syndrome in patients with Shiga toxin–producing E coli (STEC).

   4. Antiemetics

   5. Diet

      1. BRAT diet (banana, rice, applesauce, toast) is often recommended.

      2. Dairy products should be avoided. (See discussion below).

2. Antimicrobial therapy

   1. Treatment other than supportive care is not necessary for norovirus-like illnesses.

   2. Empiric antimicrobial therapy is recommended for diarrheal infections only ...