Bacterial Pneumonia Caused Most Deaths
in 1918 Influenza Pandemic
Implications for Future Pandemic Planning
The majority of deaths during the influenza pandemic of 1918-1919
were not caused by the influenza virus acting alone, report researchers
from the National Institute of Allergy and Infectious Diseases
(NIAID), part of the National Institutes of Health. Instead, most
victims succumbed to bacterial pneumonia following influenza virus
infection. The pneumonia was caused when bacteria that normally
inhabit the nose and throat invaded the lungs along a pathway created
when the virus destroyed the cells that line the bronchial tubes
and lungs.
A future influenza pandemic may unfold in a similar manner, say
the NIAID authors, whose paper in the Oct. 1 issue of The Journal
of Infectious Diseases is now available online. Therefore,
the authors conclude, comprehensive pandemic preparations should
include not only efforts to produce new or improved influenza vaccines
and antiviral drugs but also provisions to stockpile antibiotics
and bacterial vaccines as well.
The work presents complementary lines of evidence from the fields
of pathology and history of medicine to support this conclusion. "The
weight of evidence we examined from both historical and modern
analyses of the 1918 influenza pandemic favors a scenario in which
viral damage followed by bacterial pneumonia led to the vast majority
of deaths," says co-author NIAID Director Anthony S. Fauci,
M.D. "In essence, the virus landed the first blow while bacteria
delivered the knockout punch."
NIAID co-author and pathologist Jeffery Taubenberger, M.D., Ph.D.,
examined lung tissue samples from 58 soldiers who died of influenza
at various U. S. military bases in 1918 and 1919. The samples,
preserved in paraffin blocks, were re-cut and stained to allow
microscopic evaluation. Examination revealed a spectrum of tissue
damage "ranging from changes characteristic of the primary
viral pneumonia and evidence of tissue repair to evidence of severe,
acute, secondary bacterial pneumonia," says Dr. Taubenberger.
In most cases, he adds, the predominant disease at the time of
death appeared to have been bacterial pneumonia. There also was
evidence that the virus destroyed the cells lining the bronchial
tubes, including cells with protective hair-like projections, or
cilia. This loss made other kinds of cells throughout the entire
respiratory tract — including cells deep in the lungs — vulnerable
to attack by bacteria that migrated down the newly created pathway
from the nose and throat.
In a quest to obtain all scientific publications reporting on
the pathology and bacteriology of the 1918-1919 influenza pandemic,
Dr. Taubenberger and NIAID co-author David Morens, M.D., searched
bibliography sources for papers in any language. They also reviewed
scientific and medical journals published in English, French and
German, and located all papers reporting on autopsies conducted
on influenza victims. From a pool of more than 2,000 publications
that appeared between 1919 and 1929, the researchers identified
118 key autopsy series reports. In total, the autopsy series they
reviewed represented 8,398 individual autopsies conducted in 15
countries.
The published reports "clearly and consistently implicated
secondary bacterial pneumonia caused by common upper respiratory
flora in most influenza fatalities," says Dr. Morens. Pathologists
of the time, he adds, were nearly unanimous in the conviction that
deaths were not caused directly by the then-unidentified influenza
virus, but rather resulted from severe secondary pneumonia caused
by various bacteria. Absent the secondary bacterial infections,
many patients might have survived, experts at the time believed.
Indeed, the availability of antibiotics during the other influenza
pandemics of the 20th century, specifically those of 1957 and 1968,
was probably a key factor in the lower number of worldwide deaths
during those outbreaks, notes Dr. Morens.
The cause and timing of the next influenza pandemic cannot be
predicted with certainty, the authors acknowledge, nor can the
virulence of the pandemic influenza virus strain. However, it is
possible that — as in 1918 — a similar pattern of viral
damage followed by bacterial invasion could unfold, say the authors.
Preparations for diagnosing, treating and preventing bacterial
pneumonia should be among highest priorities in influenza pandemic
planning, they write. "We are encouraged by the fact that
pandemic planners are already considering and implementing some
of these actions," says Dr. Fauci.
Visit http://www.PandemicFlu.gov for
one-stop access to U.S. Government information on avian and pandemic
flu.
NIAID conducts and supports research — at NIH, throughout
the United States, and worldwide — to study the causes of
infectious and immune-mediated diseases, and to develop better
means of preventing, diagnosing and treating these illnesses. News
releases, fact sheets and other NIAID-related materials are available
on the NIAID Web site at http://www.niaid.nih.gov.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.
Reference:
DM Morens et al. Predominant role of bacterial pneumonia as a cause
of death in pandemic influenza: Implications for pandemic influenza
preparedness. The Journal of Infectious Diseases DOI: 10.1086/591708
(2008).
|