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TETANUS

Definition and Introduction

Tetanus is a potentially fatal, toxin-mediated disease caused by Clostridium tetani, characterized by severe, uncontrolled skeletal muscle spasms, autonomic nervous system dysfunction, and, if untreated, respiratory failure and death. Known colloquially as "lockjaw," it is entirely preventable by vaccination, yet remains a significant global health problem, particularly in regions with low immunization coverage. The WHO reported 15,103 cases in 2018, with thousands more unreported annually, causing approximately 34,000 neonatal deaths each year (Rosen's Emergency Medicine).

Etiology and Microbiology

Clostridium tetani is a Gram-positive (variable staining in tissue), motile, rod-shaped, obligate anaerobic, spore-forming bacillus. Its spores are ubiquitous in soil, dust, and the feces of humans and animals. Spores are highly resistant to heat and chemical disinfectants and can survive in soil for months to years.

When introduced into a wound, spores may not germinate immediately. Under anaerobic conditions - created by devitalized tissue, foreign bodies, or coexisting bacteria - the spores germinate into mature bacilli. These vegetative forms develop a characteristic terminal spherical endospore, giving the organism its classic "drumstick" appearance. Only these mature vegetative bacilli produce the neurotoxin responsible for clinical disease.

C. tetani is non-invasive; it does not spread systemically. Clinical disease results entirely from toxin production at the wound site. Germination can occur without overt clinical signs of wound infection, which is why the portal of entry is sometimes trivial or inapparent (Rosen's Emergency Medicine, p. 2590).

Epidemiology and Risk Factors

The incidence of tetanus has declined dramatically in developed countries following mass vaccination programs - from 4 cases per million in the 1940s to fewer than 0.01 per million in the United States by 2010. However, the disease persists globally, especially in warm, damp climates.

Risk factors include:

Inadequate or absent immunization (the primary risk factor)
Waning immunity in the elderly (highest incidence in those >65 years; fatality approaches 50% in patients >70 years)
Injection drug use (accounts for ~50% of US cases)
Deep penetrating wounds, puncture wounds, lacerations, and abrasions
Chronic skin ulcers, abscesses, otitis media
Contaminated umbilical cord dressings in neonates (in low-resource settings)
Postoperative tetanus following intestinal operations or abortions (endogenous source - up to 10% of humans carry C. tetani in the colon)

The overall case fatality rate is approximately 18%. Cases have been reported in fully vaccinated individuals, but deaths in this group are rare (Rosen's Emergency Medicine, Harrison's).

Incubation period: 1 day to several months, with a median of 7 days (range 4-14 days). A shorter incubation period portends a worse prognosis.

Pathophysiology

C. tetani produces two toxins: tetanolysin (a hemolysin of uncertain clinical significance) and tetanospasmin, the neurotoxin responsible for all manifestations of tetanus.

Tetanospasmin is synthesized as a single polypeptide chain that is cleaved into a heavy chain (responsible for neuronal binding and internalization) and a light chain (the zinc-dependent endopeptidase that cleaves SNARE proteins and blocks neurotransmitter release).

The toxin:

Is produced at the wound site and binds to peripheral motor nerve endings.
Undergoes retrograde axonal transport to the spinal cord and brainstem.
Spreads transsynaptically to inhibitory interneurons (Renshaw cells and glycinergic/GABAergic interneurons).
Cleaves synaptobrevin (a SNARE protein), blocking the presynaptic release of inhibitory neurotransmitters - GABA and glycine.
Without inhibitory control, alpha motor neurons undergo sustained, unopposed excitatory discharge, producing the continuous muscle rigidity and reflex spasms characteristic of tetanus.

The binding of tetanospasmin at the synapse is irreversible; clinical recovery occurs only when new axonal terminals are produced - which explains the 4-6 week recovery period and why antitoxin cannot reverse already-bound toxin.

Tetanospasmin also reaches preganglionic sympathetic neurons and parasympathetic centers, producing autonomic nervous system dysfunction (ANSD) - the leading cause of death in patients who survive the early spasm phase (Rosen's, Harrison's).

Clinical Manifestations

Tetanus presents in four clinical forms:

1. Generalized Tetanus (most common, ~80% of cases)

The classic and most common presentation, resulting in spasms of agonist and antagonist muscle groups throughout the body.

Early symptoms:

Trismus ("lockjaw") - masseter muscle spasm, present in 50-75% of patients; often the first symptom
Risus sardonicus - spasm of facial muscles producing a sardonic smile
Irritability, weakness, myalgias, dysphagia, hydrophobia, drooling

Progressive symptoms:

Generalized uncontrollable muscle spasms, occurring spontaneously or triggered by minor stimuli (touch, light, noise, IV cannulation)
Opisthotonus - prolonged tonic contraction of paravertebral and extensor muscles arching the whole body
Spasms can cause vertebral and long-bone fractures, tendon rupture, and shoulder/temporomandibular joint dislocations
Laryngeal/respiratory muscle spasm - the most common direct cause of death; causes apnea, hypoxia, and respiratory arrest

Late (week 2 onwards):

Autonomic nervous system dysfunction (ANSD): fluctuating tachycardia/bradycardia, hypertension/hypotension, hyperpyrexia, profuse sweating, gastrointestinal stasis, increased tracheal secretions
Cardiovascular death is the major risk in patients who survive the acute spasm phase

Crucially, patients remain completely lucid throughout unless chemically sedated. This distinguishes tetanus from encephalitis.

The illness progresses over approximately 2 weeks; if the patient survives, recovery is complete after 4 weeks or more.

2. Localized Tetanus

Persistent muscle spasms restricted to the site of injury. Mortality is lower than generalized tetanus. It may reflect partial immunity to tetanospasmin. Can last weeks to months and may progress to generalized tetanus.

3. Cephalic Tetanus

A rare variant of localized tetanus following facial trauma, otitis media, or head wounds. Cranial nerve palsies (most commonly CN VII, mimicking Bell palsy; also CN III, IV, IX, X, XII) precede or accompany trismus and spasms. One-third resolve completely; the remainder progress to generalized tetanus. Mortality: 15-30%.

4. Neonatal Tetanus

Generalized tetanus of the newborn, occurring in countries where maternal immunization is inadequate and contaminated materials are used to cut/dress the umbilical cord. Symptoms begin in the first week of life: inability to suck, poor feeding, irritability, and generalized spasms. Mortality approaches 100% without medical support. With basic care, mortality can be reduced to <50%.

Ablett Classification of Severity

The Ablett score classifies tetanus severity into four grades:

Grade	Severity	Features
I	Mild	Mild trismus, no spasms, no dysphagia, no respiratory compromise
II	Moderate	Moderate trismus, moderate rigidity, short spasms, mild tachycardia, mild tachypnoea
III	Severe	Severe trismus, generalized spasms, prolonged apnoeic episodes, severe autonomic disturbance
IV	Very severe	Grade III + severe autonomic disturbance

(Harrison's Principles of Internal Medicine, 22E)

Diagnosis

Tetanus is a clinical diagnosis. No laboratory tests confirm or exclude it.

Clinical diagnosis is based on:

Trismus, risus sardonicus, opisthotonus, and reflex spasms
History of a wound or predisposing condition
Absence of altered consciousness (helps differentiate from encephalitis)

Investigations (limited value):

Wound culture: positive in only one-third of cases; a positive result does not confirm toxin-producing strain
Serum anti-tetanus IgG: levels >0.1 IU/mL (by ELISA) are considered protective and argue against tetanus; below this threshold, a bioassay may help but negative results do not exclude diagnosis
PCR/recombinase polymerase amplification for tetanus neurotoxin gene: promising but not routine
Lumbar puncture: to exclude meningitis in neonates when diagnosis is uncertain
CT brain: to exclude intracranial pathology
Serum calcium: to exclude hypocalcaemia
EMG: may be useful for localized/cephalic tetanus

Differential diagnosis:

Strychnine poisoning - the only condition that truly mimics generalized tetanus (antagonizes glycine but not GABA; no trismus)
Dystonic reactions to antidopaminergic drugs (responsive to benztropine/diphenhydramine)
Stiff person syndrome
Neuroleptic malignant syndrome
Hypocalcaemia (neonatal)
Peritonitis (abdominal rigidity - but not continuous)
Rabies (brainstem dysfunction, hydrophobia - but no trismus)
Meningoencephalitis (altered consciousness)
Oropharyngeal infections (causing trismus)

Management

Management of established tetanus involves five parallel strategies: wound care, antibiotic therapy, antitoxin administration, control of spasms, and autonomic management. Patients with moderate-to-severe tetanus require intensive care unit admission.

1. Supportive / ICU Care

Nurse in a calm, quiet environment with minimal sensory stimuli (dimmed lights, reduced noise, gentle handling) to minimize stimulus-triggered spasms
Secure the airway early - tracheostomy is preferred over endotracheal intubation in severe tetanus, because laryngeal spasm and pharyngeal rigidity make intubation difficult and dangerous
Mechanical ventilation as required (patients may need ventilator support for several weeks)
NG feeding for nutrition; prevention of aspiration

2. Wound Care

Identify, debride, and clean the entry wound to remove devitalized (anaerobic) tissue and prevent further toxin production
Wound care should be performed several hours after antitoxin administration to minimize systemic toxin release during debridement
Failure to remove devitalized tissue may result in prolonged or recurrent tetanus

3. Antibiotic Therapy

Metronidazole (400 mg rectally or 500 mg IV every 6 hours for 7 days) is the drug of choice - it kills vegetative C. tetani without affecting GABA receptors
Penicillin G (100,000-200,000 IU/kg/day) is an alternative, but theoretically may worsen spasms due to its GABA receptor binding activity; associated with increased mortality in one study

4. Antitoxin

Human Tetanus Immunoglobulin (HTIG): preparation of choice; given as a single IM dose of 500-5000 IU; neutralizes circulating (unbound) toxin
Equine antitoxin: widely available in low/middle-income countries; dose 10,000-20,000 U IM after hypersensitivity testing; a recent RCT from Vietnam showed no significant outcome difference between IM equine antitoxin and HTIG
Antitoxin cannot reverse toxin already bound to nerve terminals; it only prevents further binding
Additional intrathecal HTIG has shown no benefit in trials

5. Control of Spasms

Benzodiazepines (diazepam, midazolam): first-line agents for spasm control; patients tolerate high doses
- Diazepam: intermittent or continuous; risk of hyperosmolarity and lactic acidosis at high doses
- Midazolam: preferred for continuous infusion (fewer side effects)
- Propofol: IV infusion for refractory spasms and sedation
Neuromuscular blocking agents (NMBAs): non-depolarizing agents (vecuronium, pancuronium, rocuronium) when sedatives alone are insufficient; require mechanical ventilation
IV Magnesium sulfate: acts as a muscle relaxant and also attenuates autonomic disturbance; maintain plasma levels of 2-4 mmol/L

6. Autonomic Management (ANSD)

Hypertension/tachycardia: magnesium sulfate (first line); short-acting beta-blockers (labetalol, esmolol, propranolol) or calcium channel antagonists if magnesium is inadequate
Hypotension/bradycardia (parasympathetic predominance): vasopressors required
Avoid high-dose propranolol (risk of sudden cardiac death from unopposed alpha-adrenergic activity)

7. Active Immunization

Tetanus does not confer immunity (the toxin dose causing disease is sub-immunogenic). Therefore, active immunization with tetanus toxoid must be given during the illness to prevent future episodes (given at a separate site from antitoxin)

Prevention

Wound Prophylaxis

Following any wound, tetanus prophylaxis depends on immunization history and wound characteristics:

Clean, minor wounds:
- Fully immunized (≥3 doses, booster within 10 years): no prophylaxis needed
- Incompletely immunized or unknown: tetanus toxoid
Tetanus-prone wounds (contaminated with soil/feces, devitalized tissue, puncture wounds, burns, >6 hours old):
- Fully immunized (booster within 5 years): no prophylaxis
- Incompletely immunized: tetanus toxoid + HTIG (250-500 IU IM at separate site)

Routine Immunization Schedule

Primary series: DTP vaccine at 2, 3, 4 months of age (or equivalent schedule)
Booster at school entry and adolescence
Booster every 10 years in adults (Td/Tdap)
Maternal immunization: key to preventing neonatal tetanus - two doses of tetanus toxoid in pregnancy confer passive immunity to the neonate via placental transfer

Prognosis

Prognosis depends on:

Incubation period: shorter = worse prognosis
Period of onset (time from first symptom to first spasm): shorter = worse
Age (elderly have higher mortality)
Previous immunization status
Comorbidities
Sophistication of medical care available

Overall mortality in established tetanus is approximately 45% (Bailey & Love). With appropriate intensive care, this can be significantly reduced. In neonatal tetanus without support, mortality approaches 100%. Long-term physical sequelae in survivors are rare; the most common persistent problem is psychological trauma from the illness and its treatment.

Complications

Respiratory failure from laryngospasm or respiratory muscle spasm (most common early cause of death)
Autonomic dysfunction with fatal cardiac dysrhythmias (most common late cause of death)
Vertebral fractures, long-bone fractures, tendon ruptures from forceful spasms
Rhabdomyolysis and acute renal failure
Deep vein thrombosis and pulmonary embolism
Aspiration pneumonia
Peptic ulcers, ileus, intestinal perforation
SIADH
Secondary wound infection
Hemolysis

Summary

Tetanus is a toxin-mediated neuromuscular disease caused by Clostridium tetani that remains a global killer despite an effective vaccine. The pathophysiology centers on tetanospasmin blocking inhibitory neurotransmitter (GABA and glycine) release, causing unopposed motor excitation and reflex spasms. Clinical diagnosis is paramount - trismus, risus sardonicus, and opisthotonus in a lucid patient are hallmarks. Management requires simultaneous wound debridement, antitoxin (HTIG), metronidazole, spasm control with benzodiazepines, airway protection (often tracheostomy), and ICU-level autonomic management. Prevention through vaccination remains the cornerstone of control; the disease is almost entirely preventable.

Sources: Harrison's Principles of Internal Medicine 22E (2025); Rosen's Emergency Medicine 9E; Bailey and Love's Short Practice of Surgery 28E

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