Tetanus

Tetanus is an acute and often fatal disease induced by the tetanospasmin, an exotoxin produced by Clostridium tetani, a gram-positive anaerobic bacillus (Bleck, 2005; CDC, 2012). C. tetani is sensitive to heat and not viable under aerobic conditions (CDC, 2012). In contrast, the spores of C. tetani are resistant to heat and antiseptics and are widely present in soil and in the intestines and faeces of animals (e.g. horses, sheep and dogs). Tetanus is primarily contracted via contaminated wounds and is not contagious. Effective vaccination programmes significantly reduced the burden of tetanus. Globally around 800 000 to 1 000 000 people die of tetanus each year (Dietz, 1996). Around 90% of all deaths occur in developing countries which are largely affected by tetanus and especially neonatal and maternal tetanus. In developed countries, high-risk groups, such as unvaccinated persons and injecting drug users, are prone to infection with C. tetani (CDC, 2012). The proportion of asymptomatic/subclinical infections is unknown but it can be assumed that cases of tetanus are symptomatic in nearly 100% of those infected. The first symptoms of tetanus appear after an average incubation period of eight days (range: 3–21 days) (CDC, 2012). The duration of the symptomatic disease for generalised, localised and cephalic tetanus is two to three weeks (CDC, 2012).

Health outcomes/states associated with tetanus infection

The clinical features of acute tetanus infections can be subdivided into three health states that are observed in developed countries. A fourth type, tetanus neonatorum is a specific form of generalised tetanus that affects neonates and is mostly observed in the developing world with a high case fatality of up to 90% (Roper, 2007). As neonatal tetanus has been eliminated in Europe this health outcome is not considered in our outcome tree and model.

The distribution of the three health states is set according to the observed risk of developing the different forms of acute infection in USA (Bardenheier, 1998): 81% were generalised; 13% localised and 6% cephalic.

Localised tetanus

Localised tetanus is an uncommon health state of tetanus. Localised tetanus appears as a persistent contraction of muscles in the injured area, commonly preceding generalised tetanus, and lasts around two to three 3 weeks (CDC, 2012).

Generalised tetanus

The most common health state of tetanus infection is generalised tetanus. The probability of developing generalised tetanus after initial infection is around 80% (CDC, 2012; Bardenheier, 1998; Guilfoile, 2008). The symptoms of generalised tetanus are trismus or lockjaw in the early stages, developing into stiffness of the neck, difficulty in swallowing and rigidity of abdominal muscles. Further, unspecific symptoms such as elevated temperature, sweating, elevated blood pressure, and episodic rapid heart rate may occur. Generalised tetanus can last for 3-4 weeks and full recovery may take several months (CDC, 2012).

Cephalic tetanus

Cephalic tetanus is another uncommon health state involving the cranial nerves. The same duration has been assumed for this health state as for localised tetanus: 2–3 weeks.

Further complications and case fatality proportion

In cases of cephalic tetanus otitis media may occur (CDC, 2012). Long-term sequelae/disabilities from tetanus are not reported in the literature.

The overall mortality rate of tetanus ranges from 28/100 000 in developing countries to 0.1/100 000 in developed countries such as the USA. The case fatality proportion ranges between 5 and 55% (Guilfoile, 2008; Brook, 2004; Cook, 2001; Farrar, 2000; Kanchanapongkul, 2001; Miranda-Filho Dde 2004; Saltoglu, 2004; Sanford, 1995; Thwaites, 2004; Trujillo, 1987). Mortality from tetanus is clearly dependent on age, immune status and vaccination. People over 60 years of age or unvaccinated persons have an elevated lethality of 18 and 22%, respectively. In the model, the mortality rate following symptomatic cases was set at 11% (CDC, 2012; Bardenheier, 1998).

Model input summary

Table 1. Transition probabilities used in the outcome tree

Health outcome
(Health state)

Distribution of health states in health outcome

Transition probability

Source/assumption

Symptomatic infection

(Localised tetanus)

(Generalised tetanus)

(Cephalic tetanus)

 

13%

81%

6%

 

 

Bardenheier, 1998

Fatal cases

 

 

11%

CDC, 2012

Bardenheier, 1998

Table 2. Disability weights and duration

Health outcome
(Health state)

Disability Weight (DW) (Haagsma, 2015)

Duration

DW

Label

In years

Source

Symptomatic infection

(Generalised tetanus)

(Localised tetanus)

(Cephalic tetanus)

0.421 (0.377-0.477)

0.011 (0.008-0.014)

0.053 (0.042-0.064)

Motor impairment, severe

Motor impairment, mild

Motor impairment, moderate

0.06-0.08

0.04-0.06

0.04-0.06

CDC, 2012

CDC, 2012

CDC, 2012

Assumed same as for localised

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