石和田 稔彦

INTRODUCTION: Respiratory syncytial virus (RSV) is one of the most common causes of lower respiratory tract infections in children aged <5 years and is associated with long-term respiratory morbidities such as recurrent wheezing and asthma, decreased lung function, and allergic sensitization. The objective of this review was to evaluate the epidemiology and burden of RSV infection in the pediatric population in Japan. METHODS: Studies indexed in PubMed and ICHUSHI databases during January 2010-December 2020 were manually reviewed. Data on proportion of RSV infections, seasonality, length of stay (LoS), mortality, medical expenses, and palivizumab use were extracted from the selected articles. RESULTS: Ninety-three articles were included (PubMed, 64; ICHUSHI, 29). The proportion of patients/samples with an RSV infection was 5.5%-66.7%, and 6.0%-29.9% in the inpatient and outpatient departments, respectively. RSV infections generally occurred during autumn/winter; however, recently the peak has shifted to summer. The LoS was variable and depended on factors such as age, infection severity, wheezing, and RSV subgroups. Mortality rates varied from <1% to 19% depending on the infection severity. The average daily hospitalization and intensive care unit cost was JPY 34,548 while intensive care unit incurred an additional cost of JPY 541,293. Palivizumab was indicated for high-risk infants and 0%-3% of patients required hospitalization despite palivizumab use. CONCLUSIONS: RSV imposes a significant burden on the Japanese healthcare system, suggesting a need to create awareness among caregivers of children, pregnant women and healthcare professionals to ensure early recognition of infection and adequate treatment or prophylaxis.

We conducted a systematic review of the literature to evaluate the reported epidemiology and burden of invasive pneumococcal disease (IPD) and pneumococcal pneumonia (PP) among children and adults aged 6-64 years in Japan. Studies published from Japan between September 2009 and September 2019 and indexed in the MEDLINE/PubMed or ICHUSHI databases were evaluated. A majority of the studies reported overlapping age ranges, including children aged <6 years and adults aged >64 years. According to the national surveillance data, 19% of the IPD cases were patients aged 5-59 years, and an increasing trend in IPD cases was reported from 2013 to 2017. Comorbidities were consistent with those reported by the Advisory Committee on Immunization Practices. Deaths from IPD appeared to increase nearly 3-fold between 2013 and 2017. Overall, both 13-valent pneumococcal conjugate vaccine (PCV13) and 23-valent pneumococcal polysaccharide vaccine (PPSV23) coverage was higher for IPD compared with PP. All the serotypes known to be prominent in Japan were also identified as common serotypes (3, 6A, 19A: PCV13 serotypes; 12F: outbreak serotype; 15A, 35B: drug-resistant serotypes). This systematic literature review suggests a substantial burden of IPD and PP in Japanese children and adults aged 6-64 years. The burden of comorbidities, hospitalizations, and mortality was particularly high among adults. Concerted pneumococcal vaccination strategies may help to reduce the incidence and burden of IPD and PP in this large proportion of the Japanese population.

肺炎球菌結合型ワクチンの普及後、肺炎球菌の血清型が変化してきていることが報告されている。今回、2014〜2016年度にA地区3ヶ所の保育園とB地区1ヶ所の保育園に通園していた児の上咽頭培養から分離された肺炎球菌(計133株)の薬剤感受性と血清型推移について調査した。結果、ペニシリン感受性の推移はPSSPの割合が増加していた。7価肺炎球菌結合型ワクチン含有血清型は2014年度と2015年度に各1株(いずれも血清型19F)が分離されたのみであった。13価肺炎球菌結合型ワクチンに含まれる血清型19Aは、2014年度に12株分離されていたが、2015年度以降は1株のみであった。インフルエンザ菌ABPC感受性の推移についても調査したところ、肺炎球菌と同様に感受性良好な株の割合が増加している傾向が認められた。

生後7ヵ月女児。生後2・3・4ヵ月にHibワクチンおよび7価肺炎球菌結合型ワクチンを同時接種した。今回、午前中から37℃の発熱と哺乳不良を認め、夜になると38.2℃に上昇し、嘔吐と活気不良を認めたため救急外来受診となった。脳脊髄検査にて細胞数増加を認め、細菌性髄膜炎と診断され、抗菌薬治療が行われたが、経過中に硬膜下膿瘍とくも膜下膿瘍を合併し、開頭ドレナージ術による治療が施行された。本症例においてはのちにインフルエンザ菌の血清型はf型と判明したが、Hib感染症の防御抗体である抗PRP抗体は急性期においても9μg/mlと高値あった。しかし、Hibワクチンではインフルエンザ菌f型による髄膜炎は予防できず、これが発病に至った原因と考えられた。尚、Hibワクチンが早期に導入された欧米ではb型の減少に伴い非b型による侵襲性感染症の割合が増加しており、本症例と同じf型の症例報告も散見される。これまで我が国においては検索し得た範囲ではf型の報告はないが、今後は欧米と同様な傾向を示すと推測され、侵襲性感染症から分離されるインフルエンザ菌の血清型解析を積極的に行っていく必要があると考えられた。