What is gastroenteritis?
Gastroenteritis is inflammation of the lining of the digestive tract. Most commonly it is caused by some form of infection, usually by bacteria, viruses or parasites.
Symptoms of gastroenteritis usually come on quickly. Common symptoms include: loss of appetite, nausea, diarrhoea, vomiting, abdominal cramping and loud stomach sounds. The biggest risk factor associated with gastroenteritis is dehydration, brought on by excessive vomiting and/or diarrhoea. For most healthy adults, this is not a major concern, but in small children or the elderly or debilitated it may pose a more serious health risk. If ever in doubt, see your healthcare professional.
What causes gastroenteritis?
Viruses
The two most common types of viruses that cause gastroenteritis are rotavirus and norovirus. They infect the cells lining the wall of the small intestine and cause fluids and minerals to leak into the digestive tract. This causes watery diarrhoea. The incubation period for these viruses is between 1-3 days.
Rotavirus is very contagious and commonly effects small children. It is passed on by contact with infected faeces which come in to contact with the mouth of an uninfected person (called the faecal oral route). It sounds revolting but it can happen remarkably easily! In adults rotavirus is usually mild. Interestingly, in temperate climates it seems to spread more easily in winter.
Norovirus is also highly contagious and is sometimes seen in large outbreaks of waterborne or food-borne infection. It can also be transferred person to person and is the main cause of sporadic gastroenteritis in adults and epidemic gastroenteritis in all age groups. It affects older children and adults most commonly, and infections are not seasonal like rotavirus.
Other less common viral causes of gastroenteritis include astrovirus, adenovirus, and cytomegalovirus and enterovirus in people with poor immunity.
Bacteria
Harmful bacteria are less likely to cause gastroenteritis than viruses and are most commonly found in contaminated food or water, so are more easily preventable with good hygiene practices. Bacteria are responsible for what we know as food poisoning.
The types of bacteria most commonly responsible for gastroenteritis include: Salmonella, Campylobacter, Shigella and E. coli.
Bacteria infect our digestive tract using different methods depending on the type. Some types stick to the cells lining the intestines and don't invade; they produce toxins that stop the intestinal cells from absorbing nutrients and make water and minerals travel out of the cells and into the intestines causing watery diarrhoea. Other types of bacteria release a toxin in contaminated food, and after we eat it, it is the toxin that makes us sick, not the actual bacteria. Another method of bacterial infection is when the bacteria enter the cells of the intestine and cause microscopic ulcerations that result in fluid loss.
Parasites
Parasites can also cause gastroenteritis, and the most common ones are Giardia and Cryptosporidium.
Giardia attaches to or invades intestinal cells and can reduce nutrient absorption, cause nausea, vomiting and diarrhoea, and create a general feeling of being unwell. Nutritional deficiencies can occur if the infection is ongoing and untreated. It is most commonly transmitted in contaminated water and person to person (often in daycare centres!).
Cryptosporidium is usually transmitted in water, and infection generally resolves itself in about two weeks in healthy people. The most common symptom is watery diarrhoea, though sometimes abdominal cramps, nausea and vomiting may be present.
Now that you know what gastroenteritis is, look out for Part 2 of this article for prevention tips and further information.
References available on request