CDC Updates Estimates Of Infections, Hospitalizations, and Deaths From H1N1

 

 

# 4259

 

 

Attempts to count individual deaths from the H1N1 virus in the US ceased during the summer when it was determined that it was no longer possible to keep any kind of accurate tally.

 

 

That was expected since, even during a regular flu season, we don’t count individual flu deaths.  The oft repeated number of 36,000 flu-related deaths annually is an estimate.

 

 

In November the CDC released their estimates of the pandemic’s impact here in the US up until mid-October.  At that time, they estimated 22,000,000 people had been infected and roughly 4,000 had died.

 

In December, the CDC has updated those numbers through November 14th, and they show a significant increase over the previous numbers.  A mid-range estimate of 47 million infections and nearly 10,000 deaths.

 

Today, the CDC once again updates their estimates to carry through to the 12th of December.    Their mid-range estimates are of 55 million infections and 11,160 deaths in the US from H1N1 since April of 2009.

 

 

 

 

CDC Estimates of 2009 H1N1 Influenza Cases, Hospitalizations and Deaths in the United States, April – December 12, 2009

January 15, 2010 1:00 PM ET

April – October 17 Estimates
April – November 14 Estimates

On this Page

• Background
• The Numbers
• Table: CDC Cumulative Estimates of 2009 H1N1 Cases and Related Hospitalizations and Deaths from April-December 12, 2009
• Method to Estimate 2009 H1N1 Cases, Hospitalizations and Deaths
• Background Emerging Infections Program
• Seasonal Influenza-Associated Hospitalizations in the United States
• Seasonal Influenza-Associated Deaths
• Under-Counting of Flu-Related Deaths
• Related Links

Background

Estimating the number of individual flu cases in the United States is very challenging because many people with flu don’t seek medical care and only a small number of those that do seek care are tested. More people who are hospitalized or die of flu-related causes are tested and reported, but under-reporting of hospitalizations and deaths occurs as well. For this reason CDC monitors influenza activity levels and trends and virus characteristics through a nationwide surveillance system and uses statistical modeling to estimate the burden of flu illness (including hospitalizations and deaths) in the United States.

When the 2009 H1N1 flu outbreak began in April 2009, CDC began tracking and reporting the number of laboratory-confirmed 2009 H1N1 cases, hospitalizations and deaths as reported by states to CDC. These initial case counts (which were discontinued on July 24, 2009), and subsequent ongoing laboratory-confirmed reports of hospitalizations and deaths, are thought to represent a significant undercount of the actual number of 2009 H1N1 flu cases in the United States. A paper in Emerging Infectious Diseases authored by CDC staff entitled “Estimates of the Prevalence of Pandemic (H1N1) 2009, United States, April–July 2009” reported on a study to estimate the prevalence of 2009 H1N1 based on the number of laboratory-confirmed cases reported to CDC. Correcting for under-ascertainment, the study found that every case of 2009 H1N1 reported from April – July represented an estimated 79 total cases, and every hospitalized case reported may have represented an average of 2.7 total hospitalized people. CDC then began working on a way to estimate, in an ongoing way, the impact of the 2009 H1N1 pandemic on the U.S. in terms of 2009 H1N1 cases, hospitalizations and deaths. CDC developed a method to provide an estimated range of the total number of 2009 H1N1 cases, hospitalizations and deaths in the United States by age group using data on flu associated hospitalizations collected through CDC’s Emerging Infections Program.[e1]

The Numbers

(Print table)

On November 12, 2009 CDC provided the first set of estimates on the numbers of 2009 H1N1 cases and related hospitalizations and deaths in the United States between April and October 17, 2009.

Estimates from April – October 17, 2009:

• CDC estimated that between 14 million and 34 million cases of 2009 H1N1 occurred between April and October 17, 2009. The mid-level in this range was about 22 million people infected with 2009 H1N1.
• CDC estimated that between about 63,000 and 153,000 2009 H1N1-related hospitalizations occurred between April and October 17, 2009. The mid-level in this range was about 98,000 H1N1-related hospitalizations.
• CDC estimated that between about 2,500 and 6,000 2009 H1N1-related deaths occurred between April and October 17, 2009. The mid-level in this range was about 3,900 2009 H1N1-related deaths.

Updated Estimates from April – November 14, 2009

Using the same methodology CDC updated the estimates to include the time period from April through November 14, 2009 on December 10, 2009.

• CDC estimated that between 34 million and 67 million cases of 2009 H1N1 occurred between April and November 14, 2009. The mid-level in this range was about 47 million people infected with 2009 H1N1.
• CDC estimated that between about 154,000 and 303,000 2009 H1N1-related hospitalizations occurred between April and November 14, 2009. The mid-level in this range was about 213,000 H1N1-related hospitalizations.
• CDC estimated that between about 7,070 and 13,930 2009 H1N1-related deaths occurred between April and November 14, 2009. The mid-level in this range was about 9,820 2009 H1N1-related deaths.

Updated Estimates from April – December 12, 2009

Using the same methodology CDC has updated the estimates to include the time period from April through December 12, 2009.

• CDC estimates that between 39 million and 80 million cases of 2009 H1N1 occurred between April and December 12, 2009. The mid-level in this range is about 55 million people infected with 2009 H1N1.
• CDC estimates that between about 173,000 and 362,000 2009 H1N1-related hospitalizations occurred between April and December 12, 2009. The mid-level in this range is about 246,000 H1N1-related hospitalizations.
• CDC estimates that between about 7,880 and 16,460 2009 H1N1-related deaths occurred between April and December 12, 2009. The mid-level in this range is about 11,160 2009 H1N1-related deaths.

Note: Less than 5% of increases in the estimates from one reporting date to the next are the result of delayed reporting in cases, hospitalizations and deaths.

The previous estimates of 2009 H1N1 cases, hospitalizations and deaths through November 14 encompassed the peak of 2009 H1N1 activity in the United States. The latest estimates through December 12 show a modest increase in the total number of 2009 H1N1 cases, hospitalizations and deaths since the 2009 H1N1 virus emerged. The additional four weeks of flu activity data added to the previous estimate correlate with a four week period of decreasing flu activity in the United States.