Causes

Bacteria cause different illnesses depending on the site and type of organism.

Respiratory tract

Respiratory tract infections are very common and affect all ages. Most are due to viruses, infection-causing agents smaller than bacteria. Viral respiratory infections are usually self-limiting and improve without antibiotics. Bacterial infections causing sinusitis, pharyngitis (throat infection), and pneumonia are common in children, the elderly and the immune-suppressed. The death rate due to pneumonia in the elderly is about 15 percent.

Digestive tract

Many foodborne illnesses are due to bacteria or the toxins they produce. Food that is mishandled during a summer picnic or left out for several hours allows the bacteria staphylococcus aureus to proliferate and produce a toxin that causes severe nausea and vomiting. Helicobacter pylori is a bacterium that infects the stomach lining in about 80 percent of people with peptic ulcers. H. pylori is strongly associated with both the formation of ulcers and delayed healing. The exact mechanism for this is not fully known. Antibiotics are part of the treatment for peptic ulcer.

Urinary tract

Urinary tract infections occur when bacteria from the genital tract or perineal area (between the genitals and anus) contaminate the urethra (urine passageway). This occurs most commonly in sexually active women. Women are prone to UTIs during pregnancy. Postmenopausal women may develop incontinence and UTIs following hysterectomy. In addition, incomplete bladder emptying, for example, due to prostatic enlargement in men, allows bacteria to accumulate.

Nervous system

Bacterial infections of membranes covering the brain and spinal chord (bacterial meningitis) affect people of all ages, but children less than two years old are highly susceptible. About 300 people die of meningococcal meningitis in the United States each year and about 700 die of pneumococcal meningitis. The American Academy of Pediatrics recommends vaccination against two historically common causes of child meningitis - H. influenzae and S. pneumonia - starting at two months of age.

Blood (sepsis)

Sepsis is a leading cause of death mostly in the elderly or chronically ill in the United States. Severe sepsis claims 215,000 lives each year - more than breast, colon/rectal, pancreatic and prostate cancer combined. This complex syndrome, characterized by an overwhelming systemic response to infection, strikes hard and can rapidly lead to organ dysfunction and death.

Bacterial infection from virtually any site in the body can pass into the bloodstream and cause sepsis. Fever, severe shaking (rigors), hypotension (low blood pressure), coma and death can result if sepsis is not quickly and properly treated.

Bacteria also cause endocarditis, which is an infection of the inside surface of the heart chambers or valves.

More on Bacterial Infections

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This article was reviewed and updated June 2007.