COVID-19の年代別の致命率～4万例超を分析

中国における2019年の新規コロナウイルス病（COVID-19）の発生の疫学的特徴

4万4,000例を超える新型コロナウイルス感染症（COVID-19）の疫学的調査結果が報告された。2020年2月11日時点で、中国で診断された全症例の記述的、探索的分析の結果が示されている。CCDC（中国疾病管理予防センター）のYanping Zhang氏らによるChinese journal of Epidemiology誌オンライン版2020年2月17日号掲載の報告。

　著者らは、2020年2月11日までに報告されたすべてのCOVID-19症例を、中国の感染症情報システムから抽出。以下の6つの観点で分析を実施した：

（1）患者特性の要約、

（2）年齢分布と性比の分析、

（3）致命率（死亡例数/確定例数、％で表す）と

　　 死亡率（死亡例数/総観察時間、per 10 person-days[PD]で表す）の算出、

（4）ウイルスの広がりの地理的時間的分析、

（5）流行曲線の構築、

（6）サブグループ解析。

　患者特性はベースライン時に収集され、併存疾患は自己申告による病歴に基づく。症例は、確定（咽頭スワブでのウイルス核酸増幅検査陽性）、疑い（症状と暴露状況に基づき臨床的に診断された症例）、臨床診断（湖北省のみ、COVID-19と一致する肺造影像疑いの症例）、無症候（検査陽性だが、発熱やから咳などの症状がみられない症例）に分類された。

　流行曲線における発症日は、本調査中に患者が発熱または咳の発症を自己申告した日付として定義。

重症度は、

軽度:（非肺炎および軽度肺炎の症例が含まれる）、

中等度:（呼吸困難[呼吸数≧30/分、血中酸素飽和度≦93％、PaO2/FiO2比＜300、および/または24～48時間以内に＞50％の肺浸潤]）、

重度:（呼吸不全、敗血症性ショック、および/または多臓器障害）に分類された。

　主な結果は以下のとおり。

・計7万2,314例の患者記録が分析された。内訳は、

確定が4万4,672例（61.8％）、

疑いが1万6,186例（22.4％）、

臨床診断が1万567例（14.6％）、

無症候が889例（1.2％）。以下のデータはすべて確定例での分析結果。

・年齢構成は、

9歳以下が416例（0.9％）、

10～19歳が549例（1.2％）、

20～29歳が3,619例（8.1％）、

30～39歳が7,600例（17.0％）、

40～49歳が8,571例（19.2％）、

50～59歳が1万8例（22.4％）、

60～69歳が8,583例（19.2％）、

70～79歳が3,918例（8.8％）、

80歳以上が1,408例（3.2％）。

・男性が51.4％、湖北省で診断された症例が74.7％を占め、85.8％で武漢市と関連する暴露が報告された。

・重症度は、軽度が3万6,160例（80.9％）、中等度が6,168例（13.8％）、重度が2,087例（4.7％）、不明が257例（0.6％）。

・併存疾患は、高血圧が2,683例（12.8％）、 糖尿病1,102例（5.3％）、心血管疾患874例（4.2％）、慢性呼吸器疾患511例（2.4％）、がん107例（0.5％）であった。

・1,023例が死亡し、全体の致命率は2.3％。

・年齢層別の死亡数（致命率、死亡率[per 10 PD]）は、

9歳以下は無し、

10～19歳が1例（0.2％、0.002）、

20～29歳が7例（0.2％、0.001）、

30～39歳が18例（0.2％、0.002）、

40～49歳が38例（0.4％、0.003）、

50～59歳が130例（1.3％、0.009）、

60～69歳が309例（3.6％、0.024）、

70～79歳が312例（8.0％、0.056）、

80歳以上が208例（14.8％、0.111）。

・併存疾患別の死亡数は、致命率および死亡率が高い順に、

心血管疾患92例（10.5％、0.068）＞

糖尿病80例（7.3％、0.045）＞

慢性呼吸器疾患32例（6.3％、0.040）＞

高血圧161例（6.0％、0.038）＞

ガン6例（5.6％、0.036）。

なお、

併存疾患のない患者で死亡は133例発生し、致命率は0.9％、死亡率は0.005 per 10 PDであった。

・発症の流行曲線は1月23～26日頃および2月1日にピークに達し、その後減少傾向にある。

・COVID-19は、2019年12月以降に湖北省から外部に広がり、2020年2月11日までに、31省すべてに広がった。

・1,716例の医療従事者が確定例に含まれ、5例が死亡している。

　著者らは、COVID-19は確定例の約81％で軽度であり、致命率は2.3％と非常に低いとしている。

1,023例の死亡のうち、過半数が60歳以上および/または併存疾患を有しており、

軽度または中等度の患者では死亡は発生していない。

しかし、COVID-19が急速に広がったことは明らかで、湖北省から中国本土の残りの地域に広がるまでたった30日しかかからなかったと指摘。多くの人が春節の長い休暇から戻った現在、流行のリバウンドに備える必要があるとしている。

The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19) in China

Zhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi. 2020 Feb 17;41(2);145-151. doi: 10.3760/cma.j.issn.0254-6450.2020.02.003.

Objective: An outbreak of 2019 novel coronavirus diseases (COVID-19) in Wuhan, China has spread quickly nationwide. Here, we report results of a descriptive, exploratory analysis of all cases diagnosed as of February 11, 2020. Methods: All COVID-19 cases reported through February 11, 2020 were extracted from China's Infectious Disease Information System. Analyses included: 1) summary of patient characteristics; 2) examination of age distributions and sex ratios; 3) calculation of case fatality and mortality rates; 4) geo-temporal analysis of viral spread; 5) epidemiological curve construction; and 6) subgroup analysis. Results: A total of 72 314 patient records-44 672 (61.8%) confirmed cases, 16 186 (22.4%) suspected cases, 10567 (14.6%) clinical diagnosed cases (Hubei only), and 889 asymptomatic cases (1.2%)-contributed data for the analysis. Among confirmed cases, most were aged 30-79 years (86.6%), diagnosed in Hubei (74.7%), and considered mild (80.9%). A total of 1 023 deaths occurred among confirmed cases for an overall case-fatality rate of 2.3%. The COVID-19 spread outward from Hubei sometime after December 2019 and by February 11, 2020, 1 386 counties across all 31 provinces were affected. The epidemic curve of onset of symptoms peaked in January 23-26, then began to decline leading up to February 11. A total of 1 716 health workers have become infected and 5 have died (0.3%). Conclusions: The COVID-19 epidemic has spread very quickly. It only took 30 days to expand from Hubei to the rest of Mainland China. With many people returning from a long holiday, China needs to prepare for the possible rebound of the epidemic.

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Are children less susceptible to COVID-19?

J Microbiol Immunol Infect. 2020 Feb 25

doi: 10.1016/j.jmii.2020.02.011 [Epub ahead of print]

Ping-Ing Lee,,∗ Ya-Li Hu, Po-Yen Chen, Yhu-Chering Huang, and Po-Ren Hsueh

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7102573/

Emerging at the end of 2019, coronavirus disease 2019 (COVID-19) has become a public health threat to people all over the world. The lower airway is the primary target of the infection for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pneumonia is always present in patients with severe COVID-19.1 , 2 Available reports to date show that COVID-19 seems to be uncommon in children.3, 4, 5, 6Recent data reported from the Chinese Centers for Diseases Control and Prevention indicated that among the 44,672 confirmed cases of COVID-19 as of February 11, 2020, 416 (0.9%) were aged 0–10 years and 549 (1.2%) aged 10–19 years.7 Exploring the underlying reasons may help understand the pathogenesis of COVID-19.

One possible reason is that children have fewer outdoor activities and undertake less international travel, making them less likely to contract the virus. The number of pediatric patients may increase in the future and a lower number of pediatric patients at the beginning of a pandemic does not necessarily mean that children are less susceptible to the infection. In fact, infants can be infected by SARS-CoV-2.8

During the 1918 outbreak of “Spanish flu,” those ≥65 years old and children ≤15 years experienced little or no change in excess mortality as compared with that of the previous influenza season. Nevertheless, those aged 15–24 and 25–44 years experienced sharply elevated death rates.9

Similarly, at the beginning of the 2009 pandemic H1N1 influenza outbreak, the percentage age distributions for mortality and morbidity for patients with severe pneumonia show a marked shift to persons between the ages of 5 and 59 years, as compared with distributions observed during previous periods of epidemic influenza.10

On the other hand, several infectious diseases are well known to be less severe in children. Paralytic polio occurred in approximately 1 in 1000 infections among infants, in contrast to approximately 1 in 100 infections among adolescents.11 As compared with young children, teenagers and adults tend to have symptomatic rubella more frequently and have systemic manifestations.11 The overall case-fatality rate of severe respiratory distress syndrome (SARS) ranges from 7% to 17%. Persons with underlying medical conditions and those older than 65 years of age had mortality rates as high as 50%. However, there was no mortality in children or in adults younger than the age of 24 years.11

The reasons for the relative resistance of children to some infectious diseases remains obscure. It was suggested that maturational changes in the axonal transport system may explain the relative resistance of immature mice to poliovirus-induced paralysis.12 Other suggested reasons include children having a more active innate immune response, healthier respiratory tracts because they have not been exposed to as much cigarette smoke and air pollution as adults, and fewer underlying disorders. A more vigorous immune response in adults may also explain a detrimental immune response that is associated with acute respiratory distress syndrome.11

A difference in the distribution, maturation, and functioning of viral receptors is frequently mentioned as a possible reason of the age-related difference in incidence. The SARS virus, SARS-CoV-2, and human coronavirus-NL63 (HCoV-NL63) all use the angiotensin-converting enzyme-2 (ACE2) as the cell receptor in humans.13 , 14 Previous studies demonstrated that HCoV-NL63 infection is more common in adults than in children.15 , 16 This finding suggests there may indeed be relative resistance to SARS-CoV-2 in children.

ACE2 expression in rat lung has been found to dramatically decrease with age.17 This finding may not be consistent with a relatively low susceptibility of children to COVID-19. However, studies show that ACE2 is involved in protective mechanisms of the lung. It may protect against severe lung injury induced by respiratory virus infection in an experimental mouse model and in pediatric patients. ACE2 also protects against severe acute lung injury that can be triggered by sepsis, acid aspiration, SARS, and lethal avian influenza A H5N1 virus infection.18

These intriguing findings suggest that children may really be less susceptible to COVID-19. It is important to elucidate the underlying mechanism that may help to manage COVID-19 patients.