破傷風

潜伏期間: 3〜21日（通常7〜10日。短いほど重症の傾向）

典型的な経過（全身性破傷風）:

• 開口障害（trismus/lockjaw）: 最初の症状として最も多い。咬筋の攣縮

• 痙笑（risus sardonicus）: 顔面筋の持続性攣縮による特徴的な表情

• 全身性の筋強直: 頸部硬直、体幹筋の板状硬直

• 後弓反張（opisthotonus）: 背筋の攣縮により体が弓なりに反る

• 発作性の有痛性筋攣縮: 外部刺激（光・音・接触）で誘発される。極めて強い疼痛を伴う

• 自律神経障害: 頻脈、血圧変動、発汗過多、不整脈（重症例の死因）

新生児破傷風:

• 哺乳困難（開口障害）、全身硬直、痙攣。発展途上国で問題

The risk of tetanus is determined primarily by vaccination status and the nature of wound exposure. Unlike most infectious diseases, tetanus has no person-to-person transmission component.

Risk factors for acquiring tetanus:

• Incomplete or absent vaccination: The single most important risk factor. In high-income countries, tetanus occurs almost exclusively in unvaccinated or under-vaccinated individuals (elderly who missed childhood vaccines, immigrants from countries with low coverage, individuals who declined vaccination).

• Wound characteristics: Puncture wounds (especially from nails, thorns, or splinters), crush injuries, wounds contaminated with soil or manure, burns, frostbite, avulsions, and compound fractures create anaerobic conditions favorable for spore germination. However, tetanus can follow minor injuries — in ~20% of cases, no wound is identified.

• Injection drug use: Particularly subcutaneous injection ("skin popping") of contaminated drugs. Wound botulism should be co-considered.

• Neonatal risk: Unclean delivery practices (cutting the umbilical cord with non-sterile instruments, applying traditional substances to the umbilical stump) in infants of unimmunized mothers.

• Surgical and procedural risk: Post-surgical tetanus (rare) following gastrointestinal surgery, dental procedures, or intramuscular injections with contaminated needles.

Risk factors for severe disease and poor outcomes:

• Age: Case-fatality rate increases sharply in neonates and in adults aged >60 years. In the elderly, both incomplete immunity and reduced physiological reserve contribute.

• Short incubation period: Incubation <7 days (and especially <48 hours between the first symptom and the first spasm — the "onset time") predicts more severe disease.

• Delayed treatment: Access to ICU care with mechanical ventilation and autonomic management is the major determinant of survival in severe cases. Resource-limited settings have CFR 50–70% vs. 10–20% in well-equipped ICUs.

• Wound proximity to CNS: Cephalic tetanus (head wounds, otitis media) may progress rapidly.

• Portal of entry: Neonatal tetanus (umbilical route) and post-abortive tetanus carry particularly high mortality.

Populations at elevated risk in high-income countries:

• Elderly (waning immunity, often >30 years since last booster)

• Agricultural workers and gardeners

• Injection drug users

• Immigrants and refugees from low-coverage countries

• 呼吸不全（喉頭攣縮、呼吸筋麻痺）：主要な死因

• 自律神経障害（頻脈、血圧変動、心停止）：重症例の死因

• 肺炎（誤嚥性、人工呼吸器関連）

• 骨折（攣縮時の椎体骨折など）

• 深部静脈血栓症・肺塞栓症

• 横紋筋融解症

致死率: 適切な集中治療下で10〜20%。高齢者・治療介入の遅れた例では高い。新生児破傷風の致死率は60〜80%。