Excerpt from Campylobacter Infections

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Background

The family Campylobacteraceae includes 2 genera: Campylobacter and Arcobacter. The genus Campylobacter includes 18 species and subspecies; 11 of these are considered pathogenic to humans and cause enteric and extraintestinal illnesses. The major pathogens are Campylobacter jejuni and Campylobacter fetus. The following Campylobacter species and subspecies are pathogenic to humans:

• Enteric
• • C jejuni subspecies jejuni
  • C jejuni subspecies doylei
  • Campylobacter coli
  • Campylobacter upsaliensis
  • Campylobacter lari
  • C fetus subspecies fetus
  • Campylobacter hyointestinalis
  • Campylobacter concisus
• Extraintestinal
• • C jejuni subspecies jejuni
  • C upsaliensis
  • C lari
  • C fetus subspecies fetus
  • C concisus
  • Campylobacter sputorum
  • Campylobacter curvus
  • Campylobacter rectus

Campylobacter pylori has been reclassified as Helicobacter pylori and is not addressed in this article (see Helicobacter Pylori Infection).

Campylobacter pathogens are small, curved, motile, microaerophilic, gram-negative rods. They vary in width from 0.2-0.9 mm and vary in length from 0.5-5.0 mm. They exhibit rapid, darting motility in corkscrew fashion using a single flagellum or 2 flagella (monotrichous, amphitrichous). They also possess a lipopolysaccharide endotoxin.

Campylobacteriosis infects humans and animals. The animal reservoir is the gastrointestinal tract of dogs, cats, and other pets that can carry the organism. Transmission of C jejuni to humans occurs by ingestion of contaminated food or water, including unpasteurized milk and undercooked poultry, or by direct contact with fecal material from infected animals or persons. The 2 types of illnesses associated with Campylobacter infections in humans are intestinal infection and extraintestinal infection. The prototype for intestinal infection is C jejuni, and the prototype for extraintestinal infection is C fetus.

Pathophysiology

Factors responsible for the diseases caused by C jejuni are not well known. Based on clinical illness, researchers have postulated 3 mechanisms, as follows:

• Adherence and production of heat-labile enterotoxins, inducing secretory diarrhea
• Invasion and proliferation within the intestinal epithelium, leading to cell damage and inflammatory response
• Translocation of the organism into the intestinal mucosa and proliferation in the lamina propria and mesenteric lymph nodes, leading to extraintestinal infections such as meningitis, cholecystitis, urinary tract infection, and mesenteric adenitis

Information on the pathogenesis of Campylobacter infections other than C jejuni is scarce. Bacteremia is more common with C fetus infection. A surface protein in C fetus inhibits the C3b binding responsible for both the serum and phagocytic resistance of the organism, making the organism resistant to the bactericidal effects of human serum. After oral ingestion, C fetus may colonize the intestinal tract, resulting in portal bacteremia. In immunocompetent hosts, the organism is phagocytosed by the reticuloendothelial cells in the liver, preventing further spread. However, in patients that have predisposing factors that might serve as a local site of infection such as a gravid uterus, bacteremia can lead to severe complications. Infants may be affected hematogenously or by ascending infection during amnionitis and premature rupture of membranes.

Frequency

United States

In the United States, 2 million symptomatic enteric Campylobacter infections are estimated per year (1% of the US population per year). Incidence in the rural population is 5-6 times higher because of increased consumption of raw milk. In 2005, the overall incidence rate of laboratory-confirmed Campylobacter infections in the United States was 12.7 cases per 100,000 population.¹ However, the incidence rate of symptomatic Campylobacter infections has been estimated to be 760-1100 cases per 100,000 population.²

International

In developing countries, C jejuni is often isolated from stools of healthy individuals and is especially common during the first 5 years of life. Isolation rates in children who are asymptomatic or in children with diarrhea range from 8-45%, with an annual incidence rate as high as 2.1 episodes of Campylobacter-associated diarrhea per child.

In developed countries, the average incidence rate of Campylobacter bacteremia is estimated to be 1.5 per 1000 patients with enteritis.

Mortality/Morbidity

• The vast majority of patients fully recover from C jejuni infection within 5 days (range, 2-10 d), either spontaneously or after appropriate antimicrobial therapy. The symptomatic Campylobacter infection–associated mortality rate in the United States is estimated to be 24 deaths per 10,000 culture-confirmed cases (200 deaths per year).
• Infection with C fetus is a concern in immunocompromised patients, pregnant women, and neonates.
• Previously healthy patients usually recover without complications.

Race

• Campylobacter infection has no race predilection.

Sex

• In individuals aged 45 years or younger, the C jejuni isolation rate is higher in males than in females. In individuals older than 45 years, no sexual predilection is reported.
• In the adult population, the male-to-female C fetus infection ratio is 3:1.
• No sex predilection is noted in children.

Age

• Individuals of any age can be infected with C jejuni enteritis. The rate of infection differs between developed and developing countries. In developed countries, the peak attack rates are in infants younger than 1 year; a second, broader peak attack rate occurs in persons aged 15-30 years. In developing countries, symptomatic infection chiefly affects children younger than 5 years and declines with age. This is likely due to the development of protective immunity secondary to a high level of exposure to the organism early in life.
• In contrast to the age-specific distribution of Campylobacter enteritis, the highest rate of bacteremia occurs in patients aged 65 years and older. In this age group, the incidence rate of Campylobacter bacteremia is 1 case per 170 intestinal infections; in children younger than 14 years, the incidence rate is 1 case per 3000 intestinal infections. Roughly 60-90% of isolates are C jejuni or C coli; 8-15% are C fetus. In children from developing countries, bacteremia appears common, occurring in 45 per 1000 cases of intestinal infection. C jejuni subspecies jejuni accounts for 41% of these infections, C jejuni subspecies doylei accounts for 24%, and C upsaliensis accounts for 5.6%.

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