Mar 12, 2010 (CIDRAP News) – The Centers for Disease Control and Prevention (CDC) has issued updated numbers of illnesses, hospitalizations, and deaths for the H1N1 pandemic, new estimates that add an additional month of statistics to the agency's calculations but only slightly increase the overall toll.
Between the flu strain's first appearance in April 2009 and Feb 13 of this year, the agency said Friday, about 59 million Americans contracted H1N1; about 265,000 were hospitalized for that flu; and about 12,000 died as a result of it.
In its last estimate a month ago, which took in cases that occurred through mid-January, the CDC said that about 57 million people had been infected, about 257,000 had been hospitalized, and about 11,690 had died.
(The agency released its most recent estimate today in parallel with its weekly count of flu cases, FluView, which updates flu surveillance for the United States to March 6. That update confirmed that deaths from pneumonia and influenza have declined, hospitalizations have receded almost to zero, and influenza-like illness remains low as a whole, with small surges in a few regions.)
The puzzle of how to estimate the toll of the pandemic, when flu incidence is always under-reported, has bedeviled the CDC since the novel H1N1 arrived. Relying on case counts and laboratory confirmations were quickly rejected for delivering significant undercounts.
In the December issue of Emerging Infectious Diseases, CDC staff published an algorithm that would allow the agency to scale up from known numbers to population-wide estimates. It suggests that every confirmed case found in the pandemic's first few months represented 79 uncounted cases, and every hospitalized flu patient was a stand-in for 2.7 hospitalizations.
The numbers released Friday confirm the particular impact that the novel H1N1, in contrast to seasonal flu strains, has on younger age-groups. Among those infected, 32% of the 59 million cases were among those younger than 18, and 90% were among those younger than 65. In the category of hospitalizations, 32% were among those younger than 18, and 90% again were among those younger than 65. Among those who died, 10% were younger than 18, and 87% were younger than 65—though, in non-pandemic years, flu affects the elderly the most severely.
Reed C, Angulo FJ, Swerdlow DL, et al. Estimates of the prevalence of pandemic (H1N1) 2009, United States, April-July 2009. Emerg Infect Dis 2009 Dec;15(12):2004-7 [Full text]