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zoom RSS 子どもは家庭内で新型インフルエンザ感染しやすい

<<   作成日時 : 2010/01/05 20:33   >>

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画像 家族内にH1N1インフルエンザ確認者が出た場合、19-50才の成人に比べて子どもは約2倍感染しやすいという。50才以上はさらに感染しにくい。ウイルスの伝播速度も相対的に低かったという。
 子どもは検査されやすいことや学校での集団発生が影響している可能性はある。 家族内接触で600人中78人が急性呼吸器症状を表した。3/4にあたる156家族は発生がなく、46世帯で1人発症、14世帯で2人以上が発症した。18才以下の家族が19-50才の家族の2倍感染した。50才以上はさらに罹りにくかった。発症までの時間は平均で2.6日だった。
 調査した家族の平均年齢は26才だったが、発症者の平均は16.5だった。伝染率13%は季節性インフルエンザの10-40%に比べて低い範囲にある。
 感染防御のための努力が実を結んだ結果かもしれない。
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新型インフル、家庭内感染率は低め…米調査
http://www.yomiuri.co.jp/science/news/20100104-OYT1T00504.htm
 【ワシントン=山田哲朗】新型インフルエンザの家庭内での感染率は、季節性に比べて低いとする調査結果を米疾病対策センター(CDC)など米英の研究者がまとめ、米医学誌ニューイングランド・ジャーナル・オブ・メディシン最新号に発表した。
 研究チームは、昨年新型インフルの患者が出た米国の216世帯の記録を調査した。その結果、二次感染した家族は全体600人のうち13%に当たる78人だけで、156世帯では二次感染がなかった。過去の研究では季節性の家庭内感染率は10〜40%とされ、比較すると新型の感染率は低い。
 ただ、新型インフルに対する啓発活動が行き届いた結果、看病する家族がふだんより手洗いを励行したり、患者を別の部屋に離したりした効果があった可能性もある。新型ウイルスの感染力が本当に弱いかどうかは分からない。
 家庭内に患者が出ても家族にうつるとは限らず、米専門家は「『家族がかかったから予防接種は不要』ということにはならない」と指摘している。
(2010年1月4日12時41分 読売新聞)
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“幼児 家庭で感染しやすい”
http://www.nhk.or.jp/news/k10014777621000.html
1月4日 19時2分
 新型インフルエンザは、季節性のインフルエンザに比べ、家庭内で感染を広げにくいものの、小さい子どもが家庭で感染する危険性は、大人の3.5倍に上るとする調査結果を、アメリカのCDC=疾病対策センターなどのグループがまとめました。
 この調査は、アメリカのCDC=疾病対策センターなどのグループが、去年新型インフルエンザの患者が出たアメリカ国内の216世帯600人を対象に行ったものです。それによりますと、患者が家庭内で感染を広げる2次感染が起きていたのは、全体の13%に当たる78人だけで、季節性インフルエンザの2次感染の割合が10%から40%になるのに比べ、低い割合にとどまっていたということです。その一方、家庭内のどの年代が感染しやすいかを見たところ、4歳以下の子どもが感染する危険性は、大人の3.52倍に上っていることがわかり、研究グループでは、感染拡大を防ぐためには、ワクチン接種など子どもへの対策が重要なことがあらためて示されたとしています。これについて新型インフルエンザに詳しい東北大学の押谷仁教授は「家庭での感染率が低いのは、手洗いなどの対策を行った結果とも考えられ、必ずしもウイルスの感染力が弱いことを意味していない。小さな子どもは感染しやすく重症化のおそれも高いので注意する必要がある」と話しています。
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Children at Greater Risk for H1N1
Study Confirms That Children, Not the Elderly, Are Most at Risk to Catch H1N1
By MICHAEL SMITH
MedPage Today North American Correspondent
Dec. 31, 2009
http://abcnews.go.com/Health/SwineFluNews/children-greater-risk-h1n1-study-confirms/story?id=9455969

A study of household transmission of the H1N1 pandemic flu has confirmed that children 18 and younger are more at risk than young adults and seniors.
Photo: Study Confirms Greater H1N1 Risk for Kids
A study of household transmission of the H1N1 pandemic flu has confirmed that children 18 and younger are more at risk than young adults and seniors.
(Getty Images)

Compared with adults ages 19 through 50, children in households where someone had confirmed H1N1 flu were twice as likely to become infected, according to Simon Cauchemez, of Imperial College London and colleagues there and at the CDC.

Adults older than 50, on the other hand, were less likely to come down with the disease, Cauchemez and colleagues reported in the Dec. 31 issue of the New England Journal of Medicine.

The study also showed that the transmission rate of the virus is relatively low, the researchers said.

Since the start of the pandemic in April, children have been seen to be at greater risk, Cauchemez told MedPage Today, but the observations might have been explained by a case-ascertainment bias, since children would be more likely to be tested than adults.

It might also have been the case that school clusters -- which played a role in the early phase of the outbreak -- were biasing observations, he said.

The current study, Cauchemez said, "narrows the assumptions we can make on why there are more children among cases," he said. It could be, he said, that children have weaker immunity to flu, or there might be social interactions that make them more vulnerable.

To help understand the age effects, as well as other factors involved in transmission, the researchers used data collected by the CDC on 938 households in which there was a confirmed or probable case of the H1N1 flu, the so-called index patient.

For this study, the researchers looked at a subset of 216 households in which the index patient reported having household contacts and data was complete for all 600 of them.

They found:

Only 78 of the 600 household contacts, or 13 percent, developed an acute respiratory illness.

In nearly three-quarters of the households -- 156 -- no other member fell ill, while one contact fell ill in 46 and two or more developed illness in 14 households.

Household contacts 18 or younger were twice as susceptible as those age 19 to 50.
Those older than 50 were less susceptible.

On average, the time between onset of symptoms in a case patient and onset in a household contact was 2.6 days.

Why The Young May Catch H1N1 More Often

The risk to younger people was reflected in the fact that the median age of all household members was 26, while the median age of those who developed an acute respiratory illness was 16.5, the researchers said.

On the other hand, children and adults with the flu were found to be equally infectious to others, they said.

The 13 percent rate of transmission is at the low end of the scale both for seasonal flu (where it ranges from 10 percent to 40 percent) and for other pandemics, Cauchemez and colleagues said.

That transmission suggests that people who have housemates infected with H1N1 shouldn't consider that they're out of the woods themselves, according to Dr. Robert Schooley, of the University of California San Diego.

"It argues that people who have had a case of presumed H1N1 in their household shouldn't assume that they have had flu and skip being vaccinated," he said in an e-mail.

He added that the low transmissibility rate might mean that people in close contact with someone with the flu did a better job of limiting contact with the sick person, largely because of the enormous publicity devoted to the pandemic.

"It is possible that people were more likely to send household members who were sick to their rooms," Schooley said, "and that the lower transmissibility was only because people were more worried about getting this strain of flu than others that circulate every year."

The finding that children are at greater risk "supports the continued effort to immunize younger people, despite the fact that the second wave has largely dropped off," according to Dr. Andrew Pavia, of the University of Utah in Salt Lake City.

But he cautioned in an e-mail that the study focused on the spring wave of the pandemic and might not completely reflect what's currently happening.

One implication of the findings may be that the emphasis on hygiene has borne fruit, according to Dr. Tracy Zivin-Tutela, of St. Luke's-Roosevelt Hospital Center in New York city.

"The emphasis in the media of hand washing, covering your sneeze and cough, and staying home while ill has all played a role in the decrease in transmissibility of this and all other viruses," she said in an e-mail. "These lessons show that we can decrease the transmission of H1N1 as well as many other respiratory viruses."

In such household studies, the researchers cautioned, the infected patient studied may be more severely affected than usual, which may mean that transmission estimates aren't representative of all cases.

They also noted that households may be more likely to enter a study if they have more cases, which would tend to increase the attack rate.

Cauchemez and colleagues acknowledged that the secondary cases in this study were not confirmed by testing, so that it's likely that some of the cases were not caused by the H1N1 flu.

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NEMJ Volume 361:2619-2627 December 31, 2009 Number 27

Household Transmission of 2009 Pandemic Influenza A (H1N1) Virus in the United States


Simon Cauchemez, Ph.D., Christl A. Donnelly, Sc.D., Carrie Reed, D.Sc., Azra C. Ghani, Ph.D., Christophe Fraser, Ph.D., Charlotte K. Kent, Ph.D., Lyn Finelli, Dr.P.H., and Neil M. Ferguson, D.Phil.

ABSTRACT

Background As of June 11, 2009, a total of 17,855 probable or confirmed cases of 2009 pandemic influenza A (H1N1) had been reported in the United States. Risk factors for transmission remain largely uncharacterized. We characterize the risk factors and describe the transmission of the virus within households.

Methods Probable and confirmed cases of infection with the 2009 H1N1 virus in the United States were reported to the Centers for Disease Control and Prevention with the use of a standardized case form. We investigated transmission of infection in 216 households ― including 216 index patients and their 600 household contacts ― in which the index patient was the first case patient and complete information on symptoms and age was available for all household members.

Results An acute respiratory illness developed in 78 of 600 household contacts (13%). In 156 households (72% of the 216 households), an acute respiratory illness developed in none of the household contacts; in 46 households (21%), illness developed in one contact; and in 14 households (6%), illness developed in more than one contact. The proportion of household contacts in whom acute respiratory illness developed decreased with the size of the household, from 28% in two-member households to 9% in six-member households. Household contacts 18 years of age or younger were twice as susceptible as those 19 to 50 years of age (relative susceptibility, 1.96; Bayesian 95% credible interval, 1.05 to 3.78; P=0.005), and household contacts older than 50 years of age were less susceptible than those who were 19 to 50 years of age (relative susceptibility, 0.17; 95% credible interval, 0.02 to 0.92; P=0.03). Infectivity did not vary with age. The mean time between the onset of symptoms in a case patient and the onset of symptoms in the household contacts infected by that patient was 2.6 days (95% credible interval, 2.2 to 3.5).

Conclusions The transmissibility of the 2009 H1N1 influenza virus in households is lower than that seen in past pandemics. Most transmissions occur soon before or after the onset of symptoms in a case patient.


Source Information

From the Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London (S.C., C.A.D., A.C.G., C.F., N.M.F.); and the Centers for Disease Control and Prevention, Atlanta (C.R., C.K.K., L.F.).

Address reprint requests to Dr. Cauchemez at the Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Pl., London W2 1PG, United Kingdom, or at s.cauchemez@imperial.ac.uk.

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