Campylobacter is a genus of bacteria which contains numerous species, at least 7 of which have been shown to infect and cause disease in humans. These bacteria may also infect animals such as cattle, sheep, pigs, birds, and domestic pets such as cats and dogs. Unlike many bacteria, and indeed most of the bacteria found on or in the human body, Campylobacter bacteria are pathogenic, meaning they routinely cause human disease and are not considered a normal part of our bacterial population.
Epidemiology and Testing for Infection
While there are numerous species of Campylobacter that have been shown to infect and sicken humans, the vast majority of such infections, estimated at over 90% of reported Campylobacter isolates, are associated with Campylobacter jejuni (some 5-10% of these may actually be caused by C. coli but since disease is clinically indistinguishable and treatment does not differ, these are rarely tested to species level). Some 2 to 4 million people in the United States alone will be sickened by C. jejuni yearly and in all likelihood the actual number is higher since many people do not seek medical advice during the course of the infection, and of those that do, few have laboratory tests performed that can determine conclusively the cause of the illness, either because physicians do not order such tests or because patients find it distasteful to collect the necessary fecal samples and therefore fail to comply.
Infection rates in the developing world can be as high as 39% of the population and massive amounts of bacteria are found in the stools of infected persons. People who develop diarrhea after travel outside of the United States, particularly in the developing world, should always seek medical advice and be certain your physician knows of your recent travel history.
Some infected persons do not develop symptoms but could still be capable of transmitting the infection.
Infection is most commonly in, but certainly not limited to, infants and young adults, with more males than females being infected. However, regardless of general epidemiologic trends ANYONE who is exposed, to even very small amounts of C. jejuni bacteria, can be infected and sickened.
Symptoms of Infection and Disease
C. jejuni causes a generally self-limiting infection, meaning that it goes away on its own without treatment with antibiotics. Most illnesses last from 2-5 days. The primary symptom is diarrhea that may be accompanied by abdominal pain, fever, and cramps. Some people may experience nausea and in some cases the diarrhea may be bloody, although in many cases this will not be visible to the naked eye and will require a trained individual to examine fecal material under a microscope to identify blood cells that may be present. The presence, or absence, of blood cannot be used to conclusively diagnose or rule-out C. jejuni infection, or infection with any other intestinal pathogen, making the use of such exams questionable.
The bacteria can be recovered in the microbiology laboratory, if the infection is suspected and the laboratory is asked to attempt to recover Campylobacter, because special conditions and handling are required. Since Campylobacter infection is such a common cause of diarrhea in the United States, many laboratories will routinely examine loose stool samples for these bacteria. One should never assume that Campylobacter is causing any individual case of diarrhea as the causes of this symptom are many and in most cases there is no infection present. Only a competent microbiological laboratory can definitively identify a Campylobacter infection.
In rare cases, C. jejuni can cause serious, systematic, infections in people who are immunocompromised due to other illnesses or infections, medical treatments for some diseases, or due to age. These persons may also be sickened by other Campylobacter species. These cases are rare and there have not been more than 100 reported deaths in any one year due to Campylobacter infection.
Sources of Contamination and Prevention
C. jejuni is most commonly found in raw chicken and studies of grocery store chicken meat have revealed infection rates between 20-100%. This is not surprising since C. jejuni can infect chickens without causing illness in the bird. One should, therefore, always assume that chicken meat is contaminated and it must be cooked to an internal temperature of 165 degrees F. All juices should run clear when the meat is punctured.