Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.
Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
What is the incubation period for a norovirus infection? How long are people infected with norovirus contagious?
Norovirus may have a
prolonged infection period that starts even before a patient gets sick. There is
a short lag (up to two days) between the time that people acquire the virus and
the time they get symptoms. People may be contagious during this period. All
people are contagious while they are having symptoms.
Even people who appear to have recovered completely after a norovirus
infection may continue to shed the virus for weeks in their stool and may be a
source of infection to others. People with compromised immune systems (for
example, those receiving chemotherapy or undergoing organ transplant) may shed
the virus for months.
How is a norovirus infection diagnosed?
Because the symptoms of norovirus are
similar to those of other common viral diarrheas like rotavirus, it is necessary
to do specific tests to identify the virus. Norovirus cannot be cultured in a
laboratory. However, the RNA inside the virus may be detected directly using
polymerase chain reaction (PCR) tests, and these tests are the ones that are most
commonly used. Enzyme-based immunoassays (EIA) can also be used to detect the
virus in stool samples. EIAs use special antibodies that attach to virus
particles. In addition, the Ridascreen Norovirus 3rd Generation EIA assay is set
to be approved for use by the FDA in February 2011 to detect norovirus when a
number of people have simultaneously contracted gastroenteritis and there is a
clear avenue for virus transmission, such as a shared location or food source.
However, this new test is not sensitive enough for definitive diagnosis of
norovirus infection in an individual. The CDC updated its recommendations for
use in March 2011.The human body makes antibodies against norovirus, and these
can be identified with immunoassay testing of blood samples. Unfortunately, it
takes 10 to 14 days for the body to make antibodies, so this test is not useful
for real-time diagnosis. It is also possible to see the virus particles using
electron microscopy (see figure), although this is mostly a research tool.
Once norovirus has been confirmed in an outbreak setting, it is not necessary
to test every person. Rather, people with typical symptoms are assumed to have
acquired the virus.
Abdominal pain is pain in the belly and can be acute or chronic. Causes include inflammation, distention of an organ, and loss of the blood supply to an organ. Abdominal pain can reflect a major problem with one of the organs in the abdomen such as the appendix, gallbladder, large and small intestine, pancreas, liver, colon, duodenum, and spleen.
Gastroenteritis (viral gastroenteritis, stomach flu) is an infection caused by a variety of viruses that results in vomiting and/or diarrhea. Even though it is often called the "stomach flu," it is not caused by the influenza viruses. Viruses that can cause gastroenteritis (stomach flu) include: rotaviruses, adenoviruses, caliciviruses, astroviruses, Norwalk virus, and a group of Noroviruses. Gastroenteritis is not caused by bacteria. The main symptoms of gastroenteritis include vomiting and watery diarrhea, however, headache, fever, and abdominal cramps (stomach ache) may also be present.
Diarrhea is a change is the frequency and looseness of bowel movements. Cramping, abdominal pain, and the sensation of rectal urgency are all symptoms of diarrhea. Absorbents and anti-motility medications are used to treat diarrhea.
Headaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches, and cluster headaches are considered primary headaches. Secondary headaches are caused by disease. Headache symptoms vary with the headache type. Over-the-counter pain relievers provide short-term relief for most headaches.
Dehydration is the excessive loss of body water. There are a number of causes of dehydration including heat exposure, prolonged vigorous exercise, and some diseases of the gastrointestinal tract. The best way to treat dehydration is to prevent it from occurring.
Nausea is an uneasiness of the stomach that often precedes vomiting. Nausea and vomiting are not diseases, but they are symptoms of many conditions. The causes of vomiting differ according to age, and treatment depends upon the cause of nausea and vomiting.
Although a fever technically is any body temperature above the normal of 98.6 degrees F. (37 degrees C.), in practice a person is usually not considered to have a significant fever until the temperature is above 100.4 degrees F (38 degrees C.). Fever is part of the body's own disease-fighting arsenal: rising body temperatures apparently are capable of killing off many disease- producing organisms.
Food poisoning is common, but can also be life threatening. The most common form of food poisoning is caused by bacteria and include symptoms such as fever, abdominal pain, diarrhea, nausea and vomiting.
Recreational Water Illnesses (RWIs) are caused by germs spread by breathing in mists or aerosols, swimming, or having contact with contaminated water in hot tubs, water parks, water play areas, fountains, lakes, rivers, oceans, and swimming pools. Diarrhea is the most commonly reported recreational water illness. Diarrheal illnesses are caused by germs such as Crypto, Shigella, Norovirus, E. coli, and Giardia. Prevention of water born illnesses is key to avoid infection. Avoid swallowing water and practice good hygiene habits are a must.
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