Current H1N1 Flu Virus Is Showing
Similarities to 1918 and 1957 Pandemics
In fatal cases of 2009 H1N1 influenza, the virus can damage
cells throughout the respiratory airway, much like the viruses
that caused the 1918 and 1957 influenza pandemics, report researchers
from the National Institutes of Health (NIH) and the New York
City Office of Chief Medical Examiner.
The scientists reviewed autopsy reports, hospital records and
other clinical data from 34 people who died of 2009 H1N1 influenza
infection between May 15 and July 9, 2009. All but two of the
deaths occurred in New York City. A microscopic examination of
tissues throughout the airways revealed that the virus caused
damage primarily to the upper airway -- the trachea and bronchial
tubes -- but tissue damage in the lower airway, including deep
in the lungs, was present as well. Evidence of secondary bacterial
infection was seen in more than half of the victims.
The team was led by James R. Gill, M.D., of the New York City
Office of Chief Medical Examiner and New York University School
of Medicine, and Jeffery K. Taubenberger, M.D., Ph.D., of the
National Institute of Allergy and Infectious Diseases (NIAID)
at NIH. The findings are reported in the Archives of Pathology
& Laboratory Medicine, now available online and scheduled
to appear in the February 2010 print issue.
"This study provides clinicians with a clear and detailed
picture of the disease caused by 2009 H1N1 influenza virus that
will help inform patient management," says NIAID Director
Anthony S. Fauci, M.D. "In fatal cases of 2009 H1N1 influenza,
it appears the novel pandemic influenza virus produces pulmonary
damage that looks very much like that seen in earlier influenza
The new report also underscores the impact 2009 H1N1 influenza
is having on younger people. While most deaths from seasonal influenza
occur in adults over 65 years old, deaths from 2009 H1N1 influenza
occur predominately among younger people. The majority of deaths
(62 percent) in the 34 cases studied were among those 25 to 49
years old; two infants were also among the fatal cases.
Ninety-one percent of those autopsied had underlying medical
conditions, such as heart disease or respiratory disease, including
asthma, before becoming ill with 2009 H1N1 influenza. Seventy-two
percent of the adults and adolescents who died were obese. This
finding agrees with earlier reports, based on hospital records,
linking obesity with an increased risk of death from 2009 H1N1
The researchers examined tissue samples from the 34 deceased
individuals to assess how 2009 H1N1 influenza virus damaged various
parts of the respiratory system. "We saw a spectrum of damage
to tissue in both the upper and lower respiratory tracts,"
says Dr. Taubenberger. In all cases, the uppermost regions of
the respiratory tract -- the trachea and bronchial tubes -- were
inflamed, with severe damage in some cases. In 18 cases, evidence
of damage lower down in the finer branches of the bronchial tubes,
or bronchioles, was noted. In 25 cases, the researchers found
damage to the small globular air sacs, or alveoli, of the lungs.
"This pattern of pathology in the airway tissues is similar
to that reported in autopsy findings of victims of both the 1918
and 1957 influenza pandemics," notes Dr. Taubenberger.
The researchers also examined 33 of the 34 cases for evidence
of pulmonary bacterial infections. Of these cases, 18 (55 percent)
were positive for such infections. Not all of those individuals
who had bacterial pneumonia along with 2009 H1N1 virus infection
had been hospitalized, however, indicating that some had acquired
their bacterial infections outside of a health-care setting. This
raises the possibility, say the authors, that community-acquired
bacterial pneumonia is playing a role in the current pandemic.
"Even in an era of widespread and early antibiotic use,"
write the authors, "bacterial pneumonia remains an important
factor for severe or fatal influenza."
Computerized tomography (CT) lung images were available in four
cases of pulmonary bacterial infection. In all four cases, the
CT scans showed an abnormality known as ground-glass opacity,
which are patches of rounded haze not seen in normal lung images.
It is not known, say the researchers, whether the abnormalities
detected by CT in the four cases also occur in people who have
milder H1N1 infections. They call for additional investigation
into the utility of CT scans as a tool to help clinicians identify
and better treat severe H1N1 infections.
A full list of h1n1 vaccine ingredients, alerts and warnings.
Reference Sources: 128
December 9, 2009