미국에서 2009년 4월~7월까지 신종플루의 강도(强度, Severity) : 베이지언 분석
영국과 미국의 공동연구팀은 2009년 4월~7월 위스콘신주 밀워키와 뉴욕 2개 도시의 신종플루 관련 데이터를 분석했음. 뉴욕의 데이터는 입원이나 중환자실(ICU) 입원, 기계적 인공호흡장치(mechanical ventilation) 등의 통계(중환자실 입원율, 사망율)에 활용했으며, 밀워키와 뉴욕의 인플루엔자유사환자분율(ILI)은 임상증상 발현 환자 중 입원환자의 비율의 통계에 활용했음. 이 자료들을 조합하여 신종플루의 강도(强度, Severity)를 분석했음.
연구팀은 이 자료를 토대로 연령대별 및 전체의 임상증상 발현/사망자 비율(symptomatic case-fatality ratio, sCFR), 중환자실 입원율(sCIR), 입원율(sCHR)을 분석함.
분석결과는 sCFR of 0.048% (95% 신뢰구간 [CI] 0.026%–0.096%), sCIR of 0.239% (0.134%–0.458%), sCHR of 1.44% (0.83%–2.64%)로 나왔음.
자각증상에 따른 인플루엔자유사환자분율(ILI)을 고려하면 분석결과의 수치는 7~9배 더 낮아짐. sCFR과 sCIR은 18세 이상의 연령 층에서 가장 높게 나타나며, 5~17세 연령의 어린이들에서 가장 낮게 나타남.
가장 낮은 강도의 예측에 따르면 전체 인구의 10%에서 신종플루 증상이 나타날 경우, 사망자는 1500명~2700명에 이를 것이며, 중환자실에 입원하는 환자는 6600명~11000명에 이를 것이며, 3만6천명~7만8천명이 입원할 것으로 예상됨.
가장 높은 강도의 예측에 따르면, 사망자는 7800명~29000명에 이를 것이며, 4만명~14만명이 중환자실에 입원하고, 25만~79만명이 입원하게 될 것으로 예상됨.
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The Severity of Pandemic H1N1 Influenza in the United States, from April to July 2009: A Bayesian Analysis
Anne M. Presanis1, Daniela De Angelis1,2, The New York City Swine Flu Investigation Team3, ¶, Angela Hagy4, Carrie Reed5, Steven Riley6, Ben S. Cooper2, Lyn Finelli5, Paul Biedrzycki4, Marc Lipsitch7*
Medical Research Council Biostatistics Unit, Cambridge, United Kingdom, 2 Statistics, Modelling and Bioinformatics Department, Health Protection Agency Centre for Infections, London, United Kingdom4 Department of Health, City of Milwaukee, Milwaukee, Wisconsin, United States of America, 5 Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America, 6 Department of Community Medicine and School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, 7 Center for Communicable Disease Dynamics, Departments of Epidemiology and Immunology & Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
출처 : PLoS Med 6(12): e1000207. doi:10.1371/journal.pmed.1000207
Received: September 17, 2009; Accepted: November 19, 2009; Published: December 8, 2009
http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1000207
Abstract
Background
Accurate measures of the severity of pandemic (H1N1) 2009 influenza (pH1N1) are needed to assess the likely impact of an anticipated resurgence in the autumn in the Northern Hemisphere. Severity has been difficult to measure because jurisdictions with large numbers of deaths and other severe outcomes have had too many cases to assess the total number with confidence. Also, detection of severe cases may be more likely, resulting in overestimation of the severity of an average case. We sought to estimate the probabilities that symptomatic infection would lead to hospitalization, ICU admission, and death by combining data from multiple sources.
Methods and Findings
We used complementary data from two US cities: Milwaukee attempted to identify cases of medically attended infection whether or not they required hospitalization, while New York City focused on the identification of hospitalizations, intensive care admission or mechanical ventilation (hereafter, ICU), and deaths. New York data were used to estimate numerators for ICU and death, and two sources of data—medically attended cases in Milwaukee or self-reported influenza-like illness (ILI) in New York—were used to estimate ratios of symptomatic cases to hospitalizations. Combining these data with estimates of the fraction detected for each level of severity, we estimated the proportion of symptomatic patients who died (symptomatic case-fatality ratio, sCFR), required ICU (sCIR), and required hospitalization (sCHR), overall and by age category. Evidence, prior information, and associated uncertainty were analyzed in a Bayesian evidence synthesis framework. Using medically attended cases and estimates of the proportion of symptomatic cases medically attended, we estimated an sCFR of 0.048% (95% credible interval [CI] 0.026%–0.096%), sCIR of 0.239% (0.134%–0.458%), and sCHR of 1.44% (0.83%–2.64%). Using self-reported ILI, we obtained estimates approximately 7–9× lower. sCFR and sCIR appear to be highest in persons aged 18 y and older, and lowest in children aged 5–17 y. sCHR appears to be lowest in persons aged 5–17; our data were too sparse to allow us to determine the group in which it was the highest.
Conclusions
These estimates suggest that an autumn–winter pandemic wave of pH1N1 with comparable severity per case could lead to a number of deaths in the range from considerably below that associated with seasonal influenza to slightly higher, but with the greatest impact in children aged 0–4 and adults 18–64. These estimates of impact depend on assumptions about total incidence of infection and would be larger if incidence of symptomatic infection were higher or shifted toward adults, if viral virulence increased, or if suboptimal treatment resulted from stress on the health care system; numbers would decrease if the total proportion of the population symptomatically infected were lower than assumed.
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Study confirms low mortality for swine flu
By Maggie Fox, Health and Science Editor Maggie Fox, Health And Science Editor
출처 : 로이터통신– Mon Dec 7, 6:12 pm ET
WASHINGTON (Reuters) – One of the most systematic looks yet at the swine flu pandemic confirms that it is at worst only a little more serious than an average flu season and could well be a good deal milder, researchers said on Monday.
They analyzed data from Milwaukee and New York, two U.S. cities that have kept detailed tabs on outbreaks of H1N1, to calculate a likely mortality rate of 0.048 percent.
“That is, about 1 in 2,000 people who had symptoms of pandemic H1N1 infection died,” Dr. Marc Lipsitch of Harvard University and colleagues wrote.
Probably 1.44 percent of patients with H1N1 who were sick enough to have symptoms were hospitalized, and 0.24 percent required intensive care, they added.
The findings, published in PLoS Medicine, a Public Library of Science journal, should be reassuring to public health officials and policymakers who worry that a flu pandemic could kill millions and worsen the global recession.
They do not, however, guarantee that H1N1 will not worsen, or that some other, stronger, strain of flu will not emerge.
“We have estimated … that approximately 1.44 percent of symptomatic pandemic H1N1 patients during the spring in the United States were hospitalized; 0.239 percent required intensive care or mechanical ventilation; and 0.048 percent died,” Lipsitch and colleagues wrote.
LOWER RATES
Using a different method and New York City data only, they said they calculated a much lower death rate of 0.007 percent.
Health experts agree it is impossible to count precisely how many people have been sickened by H1N1, which was declared a pandemic in June.
Few people are tested, tests are inaccurate and many people only have mild illness. So careful projections give a more accurate picture of a pandemic than actual counts of confirmed illnesses and deaths.
Lipsitch specializes in these sorts of calculations and a global estimate he did in September gave similar projections.
One open question is how many people have actually been infected. The U.S. Centers for Disease Control and Prevention estimated in November that number was 22 million Americans.
Lipsitch’s team calculated a potential range of 7,800 to 29,000 deaths.
This compares to seasonal flu, which kills 36,000 people a year and puts 200,000 into the hospital.
“To date, symptomatic attack rates seem to be far lower than 25 percent in both the completed Southern Hemisphere winter epidemic and the autumn epidemic in progress in the United States,” the researchers added in their report, published at http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1000207.
(Editing by Doina Chiacu)
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Swine flu far less severe in latest calculations
By Steve Sternberg, USA TODAY
출처 : USA Today - Dec 07 5:51 PM
http://www.usatoday.com/news/2009-12-08-swineflu08_ST_N.htm?csp=34
A team of researchers from the USA and Britain on Monday dramatically scaled back estimates of the severity of the swine flu epidemic.
The analysis suggests that the death rate from the current wave of H1N1 flu cases probably will fall in a range that extends from far lower to slightly higher than the estimate of 36,000 deaths caused by seasonal flu in a typical year.
The analysis doesn’t project how many people will contract swine flu but “how bad it will be,” says lead author Marc Lipsitch of the Harvard School of Public Health.
At the low end, the estimates suggest that for every 10% of the population to develop flu symptoms, there will be 1,500 to 2,700 deaths, 6,600 to 11,000 people in intensive care, and 36,000 to 78,000 hospitalizations. At the high end, for the same percentage of the population, swine flu could cause 7,800 to 29,000 deaths, 40,000 to 140,000 people needing intensive care, and 250,000 to 790,000 hospitalizations.
The calculations represent a marked reduction from an August report by the President’s Council of Advisors on Science and Technology. That report proposed a “plausible” death toll that could fall anywhere between 30,000 and 90,000. Lipsitch, who worked on the August report, says the earlier estimate was based on “limited data” because the researchers began their work not long after the virus first surfaced in April, when little was known about the shape of the epidemic to come.
To fill gaps, Lipsitch and his team at Harvard and Britain’s Medical Research Council used data from Milwaukee and New York City. The data confirmed that swine flu has its biggest effect on children younger than 4 and adults 18 to 64. The study appears in the Public Library of Science (PLoS) Medicine journal.
Last month, the Centers for Disease Control and Prevention released its own estimate of the scope of the epidemic. The agency says at least 22 million Americans have gotten the flu since April. About 3,900 have died, including about 540 children.
Beth Bell of the CDC says the fact that researchers used “real live data” lends credibility to the research. She says the estimates roughly agree with those released last month by the CDC.
In a separate study, researchers at the National Institute of Allergy and Infectious Diseases and the New York City Medical Examiner’s Office reported Monday that the most severe swine flu cases can damage the entire respiratory system, much like the viruses that caused the 1918 and 1957 flu epidemics. The evidence comes from a study of 34 deaths.
“It’s an insight into how flu kills,” says institute director Anthony Fauci.
