Excerpt from Campylobacter Infections

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Background

Campylobacter infections are among the most common bacterial infections in humans. They produce both diarrheal and systemic illnesses. In industrialized regions, enteric infection produces an inflammatory, sometimes bloody, diarrhea or dysentery syndrome.

Campylobacter jejuni is usually the most common cause of community-acquired inflammatory enteritis. In developing regions, the diarrhea may be watery.

Campylobacter-like organisms can produce an enterocolitis/proctocolitis syndrome in homosexual males, who are at increased risk for infections caused by Helicobacter cinaedi and Helicobacter fennelliae. C jejuni may also produce serious bacteremic conditions in individuals with AIDS. Most reported bacteremias have been due to Campylobacter fetus fetus. Campylobacter lari, which is found in healthy seagulls, has also been reported to produce mild recurrent diarrhea in children. Campylobacter upsaliensis may cause diarrhea or bacteremia, while Campylobacter hyointestinalis, which has biochemical characteristics similar to those of C fetus, causes occasional bacteremia in immunocompromised individuals.

Campylobacter organisms may also be an important cause of traveler's diarrhea, especially in Thailand and surrounding areas of Southeast Asia. In a study of American military personnel deployed in Thailand, more than half of those developing diarrhea were found to be infected with Campylobacter species.

These organisms are related to Helicobacter pylori, which was previously known as Campylobacter pylori. No reservoir other than the human gastric mucosa has been identified for H pylori.

Pathophysiology

The known routes of transmission are fecal-oral, person-to-person sexual contact, unpasteurized raw milk and poultry ingestion, and waterborne (ie, through contaminated water supplies). Exposure to sick pets, especially puppies, has also been associated with outbreaks.

Transmission occurs most commonly from infected animals and their food products. Most human infections result from the consumption of improperly cooked or contaminated foodstuffs. Chickens may account for 50-70% of infections. In most colonized animals, a lifelong carrier state develops.

The infectious dose is 1000-10,000 bacteria. Infection has occurred after ingestion of 500 organisms by a volunteer; however, illness is infrequent with a dose of less than 10,000 organisms. Campylobacter species are sensitive to hydrochloric acid in the stomach, and antacid treatment can reduce the amount of inoculum needed to cause disease.

Symptoms begin after an incubation period of up to a week. The sites of tissue injury include the jejunum, the ileum, and the colon. C jejuni appears to invade and destroy epithelial cells. C jejuni organisms are attracted to mucus and fucose in bile, and the flagella may be important in both chemotaxis and adherence to epithelial cells or mucus. Adherence may also involve lipopolysaccharides or other outer membrane components. Such adherence would promote gut colonization. PEB 1 is a superficial antigen that appears to be a major adhesin and is conserved among C jejuni strains.

Some strains of C jejuni produce a heat-labile, choleralike enterotoxin, which is important in the watery diarrhea observed in infections. The organism produces diffuse, bloody, edematous, and exudative enteritis. The inflammatory infiltrate consists of neutrophils, mononuclear cells, and eosinophils. Crypt abscesses in the epithelial glands and ulceration of the mucosal epithelium are present.

Cytotoxin production has been reported in strains from patients with bloody diarrhea. In a small number of cases, the infection may be associated with hemolytic uremic syndrome and thrombotic thrombocytopenic purpura through a poorly understood mechanism. Endothelial cell injury, mediated by endotoxins or immune complexes, is followed by intravascular coagulation and thrombotic microangiopathy in the glomerulus and the gastrointestinal mucosa.

In patients with HIV, infections may be more frequent, may cause prolonged or recurrent diarrhea, and may be more commonly associated with bacteremia and antibiotic resistance.

C fetus is covered with a surface S-layer protein that functions like a capsule and disrupts c3b binding to the organisms, resulting in both serum and phagocytosis resistance.

C jejuni infections also show recurrence in children and adults with immunoglobulin deficiencies. Acute infection confers short-term immunity. Patients develop specific immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA) antibodies in serum; IgA antibodies also develop in intestinal secretions. The severity and persistence of infection in patients with AIDS and hypogammaglobulinemia indicates that both cell-mediated and humoral immunity are important in preventing and terminating infection.

Frequency

United States

Exact figures are not available, but an estimated 2 million cases of Campylobacter enteritis occur annually, accounting for 5-7% of cases of gastroenteritis. A large animal reservoir is present, with up to 100% of poultry, including chickens, turkeys, and waterfowl having asymptomatic infections in their intestinal tracts. The major reservoirs of C fetus are cattle and sheep.

International

C jejuni infections are extremely common worldwide. Exact figures are not available. The highest national rate of campylobacteriosis was reported by New Zealand, which peaked in May 2006 at 400 per 100,000 population.¹

Mortality/Morbidity

The disease is usually self-limited without any mortality. Exact figures are unavailable, but occasional deaths occur in young, previously healthy individuals because of volume depletion and in persons who are elderly or immunocompromised.

Race

No clear racial predominance is evident.

Sex

The organism is isolated more frequently from males than females. Homosexual men appear to be at increased risk for infection with atypical Campylobacter species such as Helicobacter cinaedi and Helicobacter fennelliae.

Age

Infection can occur in all age groups.

• Studies show a peak incidence in children younger than 1 year and in persons aged 15-29 years. The highest age-specific attack rate occurs in young children, but the greatest number of positive fecal cultures occurs in adults and older children.
• Asymptomatic infection is infrequent in adults.
• In developing countries, infection is very common in the first 5 years of life. Asymptomatic infection is also more common. In Bangladesh, up to 39% of all children younger than 2 years may be infected asymptomatically.

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