Chapter 133. Tetanus (Part 1)

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Harrison's Internal Medicine Chapter 133. Tetanus Definition Tetanus is a neurologic disorder, characterized by increased muscle tone and spasms, that is caused by tetanospasmin, a powerful protein toxin elaborated by Clostridium tetani. Tetanus occurs in several clinical forms, including generalized, neonatal, and localized disease. †A contributor to HPIM since the 12th edition, Dr. Abrutyn passed away on February 22, 2007. Etiologic Agent C. tetani is an anaerobic, motile, gram-positive rod that forms an oval, colorless, terminal spore and thus assumes a shape resembling a tennis racket or drumstick. The organism is found worldwide in soil, in the inanimate environment, in animal feces,...

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Chapter 133. Tetanus (Part 1) Harrison's Internal Medicine > Chapter 133. Tetanus Definition Tetanus is a neurologic disorder, characterized by increased muscle tone and spasms, that is caused by tetanospasmin, a powerful protein toxin elaborated by Clostridium tetani. Tetanus occurs in several clinical forms, including generalized, neonatal, and localized disease. †A contributor to HPIM since the 12th edition, Dr. Abrutyn passed away on February 22, 2007. Etiologic Agent
C. tetani is an anaerobic, motile, gram-positive rod that forms an oval, colorless, terminal spore and thus assumes a shape resembling a tennis racket or drumstick. The organism is found worldwide in soil, in the inanimate environment, in animal feces, and occasionally in human feces. Spores may survive for years in some environments and are resistant to various disinfectants and to boiling for 20 min. Vegetative cells, however, are easily inactivated and are susceptible to several antibiotics, including metronidazole and penicillin. Tetanospasmin is formed in vegetative cells under plasmid control. With autolysis, the single-chain toxin is released and cleaved to form a heterodimer consisting of a heavy chain (100 kDa), which mediates binding to and entry into nerve cells, and a light chain (50 kDa), which blocks neurotransmitter release. The genome of C. tetani has been sequenced. The amino acid structures of the two most powerful toxins known, botulinum toxin and tetanus toxin, are partially homologous. Epidemiology Tetanus occurs sporadically and almost always affects unimmunized persons; partially immunized persons and fully immunized individuals who fail to maintain adequate immunity with booster doses of vaccine may be affected as well.
Although tetanus is entirely preventable by immunization, the burden of disease worldwide is great. Tetanus is a notifiable disease in many countries, but reporting is known to be inaccurate and incomplete, particularly in developing countries. As a result, the World Health Organization considers the number of reported cases to be an underestimate and periodically undertakes case/death estimates to assess the burden of disease. In 2002 (the last year for which data are available), the estimated number of tetanus-related deaths in all age groups was 213,000, of which 180,000 (85%) were attributable to neonatal tetanus. In contrast, only 18,781 tetanus cases in total and 11,762 neonatal cases were actually reported for that year. Tetanus is common in areas where soil is cultivated, in rural areas, in warm climates, during summer months, and among males. In countries without a comprehensive immunization program, tetanus occurs predominantly in neonates and other young children. It is noteworthy that international programs to eliminate neonatal tetanus have been in place for some time. In the United States and other nations with successful immunization programs, neonatal tetanus is rare (only three cases were reported in the United States during 1990–2004), and the disease affects other age groups (Fig. 133-1) and groups inadequately covered by immunization (such as nonwhites). The success of immunization in the United States is depicted in Fig. 133-2. Since 1976, fewer than 100 cases have been reported yearly. At present, the risk of tetanus in this country is highest among the
elderly. A large-scale national serologic survey performed in 1988–1994 showed that 72% of Americans ≥6 years old had protective antibody levels. In contrast, only 30% of persons >70 years old were protected. Figure 133-2 Impact of tetanus immunization in the United States, 1947–2005 (2005, provisional total). Tetanus vaccine became part of the routine childhood immunization schedule in the late 1940s. (From Centers for Disease Control and Prevention, National Immunization Program. Tetanus and Tetanus Toxoid: Epidemiology and Prevention of Vaccine-Preventable Diseases. www.cdc.gov/nip/ed/vpd2006/Slides/chap06-tetanus9.ppt. Revised January 2006. Accessed 1/30/2007.)
In the United States, most cases of tetanus follow an acute injury (puncture wound, laceration, abrasion, or other trauma). Tetanus may be acquired indoors or during outdoor activities (e.g., farming, gardening). The implicated injury may be major but can be so trivial that medical attention is not sought. In some cases, no injury or portal of entry can be identified. The disease may complicate chronic conditions such as skin ulcers, abscesses, and gangrene. Tetanus has also been associated with burns, frostbite, middle-ear infection, surgery, abortion, childbirth, body piercing, and drug abuse (notably "skin popping"). Recurrent tetanus has been reported.