Swine Flu Pandemic Hit Children the Hardest

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Elderly Population Relatively Spared, Says CDC Report, Which Cites 'Unusual Patterns' of H1N1 Flu Strain

By Bill Hendrick
WebMD Health News

Reviewed by Laura J. Martin, MD

July 29, 2010 -- The H1N1 flu strain that sparked the first influenza pandemic in four decades has caused the majority of flu cases so far in the 2009-2010 season, the CDC says.

CDC spokesman Tom Skinner tells WebMD that the so-called swine flu bug has affected the very young more than elderly people in the current influenza season, which "is not normally the case."

"We have had a lot more young people get this flu and die than in a normal flu season," Skinner says.

The CDC's Morbidity and Mortality Weekly Report for July 30, 2010, says the H1N1 strain has shown "unusual patterns of disease, disproportionately affecting children and young adults and relatively sparing the elderly."

The MMWR says the proportion of visits to health care providers for flu-like illnesses has been among the highest this season since surveillance began in 1997.

Between April 2009 and June 12, 2010, about 740,000 flu specimens were tested, and the number of laboratory-confirmed cases was about four times the average of the previous four seasons.

Of 91,152 confirmed flu cases in that period, 99.8%, or 66,916, were caused by the 2009 H1N1 pandemic strain, the MMWR says.

Between Aug. 30, 2009, through June 12, 2010, the CDC report says the peak proportion of outpatient visits to doctors for flu-like illness was among the highest seen since current record keeping.

Slideshow: Swine Flu FAQ

Swine Flu Numbers

The MMWR says that:

• From Sept. 1, 2009, through May 1, 2010, flu-associated hospitalizations for children up to age 4 was 6.7 per 10,000 and youths 5-17, 2.5 per 10,000.
• Rates for adults were 2.5 per 10,000 for people 18-49, 3.2 for those 50-64, and 2.8 for those 65 and older.
• During the entire H1N1 pandemic season through May 1, 2010, cumulative rates of hospitalization were 8.3 per 10,000 for children up to 4, 3.4 for ages 5-17, 3.0 for people 18-49, and 3.8 for those 50-64. The rate was 3.2 for people 65 and older.

"A dramatic increase in hospitalizations in the younger age groups was indicative of the influenza pandemic's impact on children," the MMWR says.

Between Aug. 30, 2009, and June 12, 2010, 279 lab-confirmed influenza-associated pediatric deaths were reported -- four times the average in the previous five influenza seasons, CDC says. The report says that:

• 52 of the deaths were of children aged 2 and under.
• 30 children between ages 2 and 4 died.
• 103 of the deaths were of children aged 5-11, and 94 were aged 12-17.
• Of the 279 deaths, 226 were associated with the 2009 pandemic H1N1 strain, 51 with influenza A of unreported subtype, and two with influenza B.

CDC estimates that 43 million to 89 million people became sick with the pandemic H1N1 strain between April 2009 and April 2010.

Researchers recommend that doctors should "remain vigilant" and consider influenza as a potential cause of respiratory illnesses during the summer.

It says influenza vaccines are being produced in greater numbers for the 2010-2011 season in part because the federal Advisory Committee on Immunization Practices voted in February 2010 to encourage immunization for all people 6 and over.

SOURCES:
Morbidity and Mortality Weekly Report, vol 59: pp 901-908.
Tom Skinner, spokesman, CDC.
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