High levels of air pollution may increase the risk of appendicitis in adults, according to the results of a study conducted in Canada and presented at the 73rd annual scientific meeting of the American College of Gastroenterology in Orlando, Florida.

The principle investigator Dr Gilaad G. Kaplan from the University of Calgary said that the study "provides epidemiologic evidence that some cases of appendicitis may be triggered by exposures to air pollutants." This relationship may explain the drop in appendicitis rates "in North America and Europe in the latter part of the twentieth century."

The researchers looked at more than 5000 patients over 18 years old who were admitted to Calgary hospitals for appendicitis between 1999 and 2006. They determined exposures to air pollution prior to admission using data from Environment Canada's National air Surveillance programme, which uses monitoring stations to collect hourly levels of ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide and other particulate matter.

Kaplan reported that in the summer months - when people were more likely to be outdoors and when more than half of the appendicitis cases occurred - "there was a modest increased risk for being admitted for appendicitis when the concentrations of ozone and nitrogen dioxide were elevated in the atmosphere."

"This is really the first time that we've made an association between the air that we breathe and the occurrence of appendicitis," said Kaplan.

He also noted that appendicitis was first recognized in 1886 by an American surgeon and the rates increased significantly around this time in industrialised countries such as Canada, the US and England.

"In developing countries, rates of appendicitis are actually quite low, but as these countries become more industrialised, we start to see the disease emerge," Kaplan added. He also noted that the pathogenesis (the origin and development) of appendicitis is still unclear.

Appendicitis is the inflammation of the appendix, which is a small extension off the side of the large bowel. The purpose of the appendix is unclear, but recent research has suggested that it may provide a home to 'friendly bacteria' that aid digestion and help fight infection. Appendicitis is usually the result of an infection or obstruction in the appendix. The cause is not known but one theory suggests that bacteria normally found in the gut invade through the wall of the appendix, as a result of weakness in the body's defenses, to cause inflammation and infection.