Epidemic meningitis - Epidemic meningitis

Among acute suppurative meningitis, the one caused by meningococcus is called epidemic meningitis, and is classified as a Class 5 infectious disease under the Infectious Disease Prevention and Medical Care Act (Infectious Diseases Act), and is legally called meningococcal meningitis. In 1945 (Showa 20), the number of reported patients exceeded 4,000, but after this peak, the number gradually decreased, and since 1980, it has been less than 30 cases per year, making it a rare disease. However, in Europe and the United States, medium-sized outbreaks with more than 1,000 cases per year are seen, and large outbreaks have been occurring repeatedly in Africa. Epidemics occur from winter to spring in temperate zones, and are more common in the hot dry season in tropical zones.

Neisseria meningitidis is a gram-negative, kidney-type diplococcus that has never been isolated from any source other than humans. It is transmitted by droplets from patients or carriers, but usually only causes asymptomatic infection of the nasopharynx and upper respiratory tract, with only a small number of people developing the disease. The incubation period is 2-4 days, and after colonizing and multiplying in the nose and throat, it reaches the meninges via the bloodstream and causes meningitis. In most cases, symptoms begin suddenly with headache, chills, high fever, and vomiting, with fever rising to 38-40°C within 1-2 days, and confusion appears early on in moderate to severe cases. Other symptoms include meningeal irritation such as neck rigidity, which causes the head to bend insufficiently, Kernig's sign, which causes the knee to be unable to be straightened even when trying to extend the leg by holding the knee, and eye symptoms such as slow light reflex and asymmetric pupils. In the early stages of the disease, herpes simplex often occurs, and petechiae are often seen. Sometimes diarrhea, lower back pain, orchitis, and salpingitis may also occur. In the severe form, in which the disease affects both adrenal glands, the disease progresses rapidly, accompanied by disseminated intravascular coagulation (DIC), marked subcutaneous bleeding throughout the body, and circulatory collapse such as cyanosis and low blood pressure. This condition is called Waterhouse-Friderichsen syndrome, and can be seen with bacteria other than meningococcus. This form of the disease is more common in children and has a high mortality rate, with death often occurring within 48 hours.

Diagnosis is based on clinical symptoms and cerebrospinal fluid tests, especially on the identification of meningococci. Penicillin-based antibiotics are the first choice for treatment. Formerly known as meningitis or epidemic cerebrospinal meningitis, this disease was feared for its high mortality rate and for the aftereffects of recovery, such as a decline in intelligence, but advances in chemotherapy have improved the prognosis.

[Noriaki Yanagishita]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

急性化膿(かのう)性髄膜炎のうち、髄膜炎菌によるものをとくに流行性髄膜炎といい、感染症予防・医療法（感染症法）により5類感染症に分類され、法律的には髄膜炎菌性髄膜炎とよばれる。1945年（昭和20）には患者届出数が4000件を超えたが、これをピークにしだいに減少し、80年以降は年30件以下となり、まれな疾患となった。しかし、欧米では年1000件以上の中規模発生がみられ、アフリカでは大発生を繰り返している。流行は、温帯では冬から春にかけてみられ、熱帯では乾期の酷暑期に多い。

　髄膜炎菌Neisseria meningitidisはグラム陰性の腎臓(じんぞう)型の双球菌で、ヒト以外からは分離されていない。患者または保菌者から飛沫(ひまつ)感染するが、通常は鼻咽腔(びいんくう)や上気道の不顕性感染にとどまり、発病するのはごく少数である。潜伏期は2～4日で、鼻やのどに定着増殖後、血行を介して髄膜に達し、髄膜炎をおこす。多くは突然に頭痛、悪寒、高熱、嘔吐(おうと)などで始まり、熱は1、2日で38～40℃まで上昇し、中等度以上の場合は早期から意識混濁がみられる。また、頭の屈曲が不十分となる項部強直や膝(ひざ)を持って下腿(かたい)を伸展させようとしても膝をまっすぐに伸ばすことができないケルニッヒ徴候などの髄膜刺激症状、対光反射遅鈍や瞳孔(どうこう)左右不同などの眼症状も現れるほか、病初期に単純性疱疹(ほうしん)を併発し、溢血斑(いっけつはん)がみられることも多い。ときに下痢や腰痛、精巣炎や卵管炎を伴うこともある。両側副腎(ふくじん)に病変が及ぶ劇症型ではとくに急激な経過をとり、播種(はしゅ)性血管内凝固症候群（DIC＝disseminated intravascular coagulation）を伴い、全身の皮下出血が顕著で、チアノーゼや血圧低下など循環系の虚脱をきたすが、これはウォーターハウス‐フリデリクセン症候群Waterhouse-Friderichsen syndromeとよばれ、髄膜炎菌以外の細菌でもみられる。この病型は小児に多くみられ、致命率が高く、48時間以内に死亡することが多い。

　診断は臨床症状のほか、髄液の諸検査、とくに髄膜炎菌を証明することで決まる。治療にはペニシリン系の抗菌薬が第一選択である。かつては脳膜炎または流行性脳脊髄膜炎とよばれ、死亡率が高く、治っても知能の低下などの後遺症がみられ恐れられたが、化学療法の進歩によって予後もよくなった。

［柳下徳雄］

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