A year of H1N1 influenza statistics

May 1, 2010

If you thought the
flu was gone by now, think again. In early April, Florida public-health
officials in southwest Collier and Lee counties were urging those who
still had not received a vaccination to get one. Four influenza deaths
in one week in March in that state (Sarasota, Miami-Dade, Volusia,
Indian River counties) prompted the plea. The CDC reports
still-circulating H1N1, especially in Alabama, Georgia, and South
Carolina. Additionally, statistics are showing that pregnant women had a
disproportionately high risk of dying from the H1N1 pandemic flu.
Although they make up only 1% of the population, they accounted for 5%
of the deaths during the first eight months of the pandemic.

1An estimated 60 million
people in the United States have been infected with the H1N1 pandemic flu since
April 2009, according to the Centers for Disease Control and Prevention (CDC).
Roughly one in five Americans (about 61 million people) were vaccinated against
the disease, the CDC reported in January in its Morbidity and Mortality
Weekly Report
. The proportion of people vaccinated was higher among those
in priority groups, including 29.4% of children ages 6 months through 18 years
and 38% of pregnant women. Of the people who were infected up to mid-December
2009; about 257,000 — most with underlying conditions like asthma — needed
hospital care; and about 12,000 died. The early rise in flu activity in October
was in contrast to non-pandemic influenza seasons. Influenza activity usually
peaks in January, February, or March. Learn more at

2A study available online in
The Journal of Infectious Diseases
for Feb. 15 suggests that in an
influenza pandemic, vaccination may not be initially available, and antiviral
prescribing may be limited, which is why scientists need to understand how
effective other measures are in preventing influenza. During the 2006-2007 flu
season, University of Michigan School of Public Health researchers assigned more
than 1,400 college-dorm students to a group wearing face masks, a group using
both masks and alcohol-based hand sanitizer, or a control group with no
intervention. Students began using the measures just after lab confirmation of
flu on campus was made and were monitored for flu-like symptoms for six weeks.
There were significant reductions (ranging from 35% to 51%) in the incidence of
flu-like symptoms when compared with the control group. The incidence of
symptoms between the hand sanitizer/mask group and the mask-only group were not
statistically different — suggesting the use of hand sanitizer did not
substantially contribute to reducing symptoms, while the masks did.

3It has been estimated that
as many as 11% of pregnant women become infected with influenza during
pregnancy. For expectant mothers, catching a mild case of the flu could stunt
their newborns' brain development, according to a new study exploring the
effects of mild influenza infections in 12 pregnant rhesus macaques compared
with seven control pregnancies. A team led by a University of Wisconsin-Madison
professor of psychology and director of the Harlow Center for Biological
Psychology reported in the Jan. 22 online edition of Biological Psychiatry
that flu infections in pregnant monkeys resulted in significant reductions in
gray matter in baby monkeys' brains, particularly in areas that, in humans, are
associated with language and the combining of information from different senses.
The new findings demonstrate that risk to expectant mothers from common disease
can shape post-natal development and elevate the risk of behavioral and
psychiatric disorders later in life. The message of the research has compelling
public-health implications: Pregnant women or those who expect to conceive
during flu season should be vaccinated. Flu vaccinations are widely regarded in
the medical community and by the CDC as safe for pregnant women.

4According to the World
Health Organization (WHO), numbers of deaths for seasonal flu are estimates.
Methods for estimating excess mortality were introduced in the 19th century to
capture flu-associated deaths that would otherwise be missed. Such estimates
have helped counter assumptions that flu is a mild illness that rarely kills.
Statistical models use data (e.g., death certificates, medical records)
indicating mortality from all causes, and compare the number of deaths during
seasonal flu epidemics with baseline data on deaths during the rest of the year.
Efforts to assess the H1N1 pandemic's severity sometimes compare numbers of
confirmed deaths with those estimated for seasonal flu, either nationally or
worldwide, and can be misleading. Accurate assessments of mortality and
mortality rates will likely be possible only one to two years after the pandemic
has peaked.

5California's Latinos,
blacks, and Native Americans have been more likely to die from A/H1N1 flu than
whites show statewide figures from the California Department of Public Health
published less than a week after Los Angeles County health officials released
data showing H1N1 influenza had disproportionately struck the county's young and
minorities. Blacks were three times and Latinos twice as likely as whites to be
hospitalized with H1N1 flu. Reasons for the higher mortality and hospitalization
rates among these minorities involve high rates of chronic health conditions
(e.g., diabetes, obesity) that put them at greater risk for flu, as does less
access to and longer waits for healthcare, and (for cultural reasons) a tendency
to wait longer to seek help — reducing chances for successful treatment with
antiviral medication. More difficult to explain is why Asians were more likely
than whites to be hospitalized with H1N1, yet are less likely to die of it.
State officials are still compiling an ethnic breakdown of those vaccinated
against H1N1 flu to determine if a connection exists between vaccinations and
lower mortality or hospitalization rates.

6WHO confirmed the H5N1 avian
flu death of a 20-year-old pregnant woman and announced a new H5N1 case in an
18-month-old boy. Egypt's health ministry confirmed that the woman was
hospitalized and treated with oseltamivir but died March 9. The boy received
oseltamivir and was in stable condition. Both patients had been exposed to sick
and dead poultry. So far this year, Egypt has reported 16 H5N1 cases, five of
which have been fatal.


7National Institute of
Allergy and Infectious Diseases researchers warn that drug resistance to H1N1
flu can happen fast. In two cases, drug-resistant H1N1 flu developed in less
than two weeks. In one, drug resistance developed after 14 days of antiviral
therapy and the other in nine days. Drug-resistant H1N1 strains had previously
been reported in patients after more than 24 days of continuous therapy. Both
patients recovered.