Campylobacter are curved rods morphologically similarto Vibrios but regarded as a separate genus, as theyhave different biochemical characteristics. There are sixspecies, of which C. jejuni and C. fetus are important humanpathogens.C. jejuni is a major cause of prolonged severe enterocolitis,frequently associated with bloody stools andabdominal pain and tenderness suggestive of peritonitis. Itis now the pathogen most frequently isolated from patientswith gastroenteritis and the incidence of infection peaksin late summer to autumn. Infection may be acquiredfrom food or drinks, but there is often a relationship withdomestic animals, a wide variety of which are normallycolonized (e.g. dogs, fowl and cattle). In the tropics. C.jejuni can often be isolated from the faeces of asymptomaticsubjects, but it frequently causes diarrhoea in childrenless than 5 years old, implying that asymptomaticinfection occurs in those with some degree of immunity.

PathogenesisThe incubation period is up to a week, this and the severityof the illness being determined by the infecting dose oforganisms. The infecting dose required to cause illness isabout 104, but this may be reduced by conditions of lowacidity in the stomach. Human bile encourages growth ofthe organism, and the small and large intestine are colonizedand the mucosa is invaded. Although toxins are produced,they are not thought to contribute to pathogenesis.C. fetus sometimes causes bacteraemia but rarely C. jejuni,usually in the very young or elderly. Excretion in the stoolscontinues for 2-3 weeks after infection in the absence ofimmunity, which causes more rapid clearance.Clinical featuresFever, headache and malaise begin 2-5 days after infection,shortly followed by diarrhoea, often with blood, crampingabdominal pain and tenderness. The severity of pain andtenderness before the onset of diarrhoea sometimessuggests an abdominal emergency, such as appendicitis.The symptoms usually resolve within a week, but in asignificant minority the duration is longer and there maybe relapse in the absence of antibiotic treatment.Guillain-Barre syndrome is an uncommon complicationof C. jejuni infection (about 1 in 2000 cases), althoughbecause the incidence of this infection is high it is linkedto nearly 50% of cases of GBS.DiagnosisThe diagnosis is established normally by microscopyand culture of stools under microaerobic conditions, butoccasionally blood culture is positive.ManagementAs with other forms of gastroenteritis, the first priority isrehydration and correction of electrolyte disturbances (seep. 280). Appropriate analgesia is required when abdominalpain is a prominent symptom. Drugs such as codeine phosphatewhich reduce gut motility should be used withcaution in the acute phase. Simple analgesics (paracetamol)may be adequate. Antibiotics are indicated for severecases when there is fever together with systemic symptoms.Erythromycin 40mg/kg/day in four doses may alleviatesymptoms in children, and it terminates the excretion oforganisms in the faeces. If treatment is clinically indicatedbefore the organism has been identified, ciprofloxacin,500 mg b.d. for adults, is more likely to improve symptomsand reduce the duration of illness, but there isincreasing resistance to quinolones which necessitates localsurveillance.ANAEROBIC BACTERIABacteroides fragilis is the most commonly encounteredpathogenic anaerobe but many others are found amongthe normal flora of the gastrointestinal and genitaltracts; these include other Bacteroides, Fusobacteria andsome anaerobic cocci, such as peptostreptococci andmicroaerophilic streptococci. Anaerobic organisms oftencause wound infection, abscesses and septicaemia inpatients who have had abdominal surgery or intestinal perforation.Antibiotic sensitivity is restricted; metronidazoleis very useful, as it is well absorbed orally or rectally andB. fragilis is usually sensitive to it. Clindamycin is alsouseful.Mixed infectionsInfection may involve several different bacteria, includinganaerobes. Abscesses associated with the bowel, especiallythe colon, or the vagina are examples. Some tissue infections,especially in debilitated patients, may also containmultiple pathogens. Severe stomatitis, one form of whichis known as Vincent's angina, commonly occurs inmalnourished patients with poor dental hygiene. Thepathogens responsible are members of the normal mouthflora, including anaerobes and spirochaetes which aresensitive to penicillin. Metronidazole is an alternativetreatment.Necrotizing fasciitis is a rapidly spreading subcutaneousinfection; it results in extensive necrosis, which may involveany part of the body. Type I is caused by mixed infectionand type II by group A streptococci (see p. 386). Type Ioccurs particularly in diabetics, common sites being on thefeet, spreading upwards, and on the perineum. Scrotalinfection is called Fournier's gangrene. The organismsinvolved are mixed anaerobic bacteria, mainly Bacteroidesor peptostreptococci. Treatment is by a combination ofaggressive surgery and antibiotics aimed mainly at anaerobes,for example clindamycin plus ampicillin.