ジフテリア

潜伏期間: 2〜5日

• 咽頭ジフテリア: 咽頭痛、微熱、灰白色の偽膜（扁桃・咽頭後壁に密着し剥離すると出血）、頸部リンパ節腫脹（「bull neck（牡牛の首）」）

• 喉頭ジフテリア: 嗄声、犬吠様咳嗽、吸気性喘鳴（stridor）、上気道閉塞

• 皮膚ジフテリア: 潰瘍性の皮膚病変（熱帯地域に多い）

• 全身性毒素症状: 心筋炎、多発神経障害（軟口蓋麻痺→嚥下障害、眼球運動障害など）

The risk of diphtheria is primarily determined by vaccination status and proximity to endemic or outbreak settings. The following factors increase the likelihood of infection and/or severe disease:

Risk factors for infection:

• Incomplete or absent vaccination: The dominant risk factor globally. In the 1990s outbreak in the former Soviet Union (>150,000 cases, >5,000 deaths), the majority of cases occurred in adults whose childhood vaccine-induced immunity had waned without booster doses.

• Living in or traveling to endemic areas: Regions with DTP3 coverage <80%, particularly sub-Saharan Africa, South Asia, and Southeast Asia

• Crowded living conditions: Military barracks, refugee camps, prisons, homeless shelters — outbreaks propagate rapidly in overcrowded settings with poor hygiene

• Close contact with a case or carrier: Household contacts of a diphtheria case have a secondary attack rate of 2–5% even in partially immunized populations

• Low socioeconomic status and poor hygiene: Both respiratory and cutaneous diphtheria are diseases of poverty

Risk factors for severe disease and death:

• Age: CFR is highest in children <5 years (up to 20%) and adults >40 years (up to 20–30%). The relatively lower CFR in older children and young adults (3–5%) reflects both immune maturity and lower membrane burden.

• Delayed antitoxin administration: Every day of delay after day 2 of illness increases mortality. Antitoxin given on day 1 is associated with ~1% CFR; by day 4+, CFR exceeds 15%.

• Extensive membrane: Membrane involving the larynx, trachea, or extending across the entire pharynx carries higher risk of airway obstruction and systemic toxicity.

• Bull-neck (severe cervical edema): Indicates massive toxin production and correlates with higher rates of myocarditis and neuropathy.

• Biotype: C. diphtheriae biotype gravis has historically been associated with more severe disease, though this correlation is not absolute.

Populations at increased risk in high-income countries:

• Adults aged >50 years (waning immunity, inadequate booster uptake — serological studies show 30–60% are below protective antibody levels)

• Immigrants and refugees from low-coverage countries

• Homeless populations (cutaneous diphtheria)

• Healthcare workers in contact with cases

• 心筋炎: 毒素による。発症後1〜2週間。致命率の最大原因。伝導障害、心不全

• 多発神経障害: 軟口蓋麻痺（鼻声、飲み込み障害）→四肢の麻痺。発症後2〜6週間。通常は回復可能

• 気道閉塞: 偽膜による窒息

• 腎障害: 毒素による尿細管壊死

致死率: 5〜10%（先進国の適切な治療下）。治療遅延・心筋炎合併例では高い。