More research needed to measure impact of co-infections on hospital
A study at Rhode Island Hospital has found that despite complications,
patients co-infected with the pandemic 2009-2010 influenza A H1N1
(pH1N1) and a second respiratory virus were not associated with worse
outcomes or admission to the hospital’s intensive care unit. The study is published online in the journal PLOS ONE.
“There is scant data in the literature regarding the incidence and
impact of simultaneous infection by two respiratory viruses,
particularly in adults,” said senior investigator Leonard Mermel, DO,
medical director of the department of epidemiology and infection control
at Rhode Island Hospital. “We compared 617 people hospitalized with
respiratory infection due to a single virus to 49 people hospitalized
with such infections due to two viruses (co-infection). Those with viral
co-infection were younger, more often had fever/chills and shortness of
breath than those with co-infection. Although patients with viral
co-infection were more likely to be treated for a secondary bacterial
pneumonia, they were not more likely to require ICU admission and they
did not have a longer length of hospital stay.”
The pandemic 2009-2010 influenza A (pH1N1) was first identified in the
U.S. in April 2009 and infected patients across the country in two
waves. There were an estimated 61 million cases of pH1N1; 274,000
hospitalizations; and 12,470 deaths associated with the pandemic -- a
significant increase in hospitalizations, and a decrease in mortality as
compared to seasonal influenza averages.
Children experienced a greater burden of disease than adults during the
pandemic, with a higher mortality rate. However, despite fewer cases in
adults, more adult patients were afflicted with serious illness.
Children also had a higher rate of co-infection, which may be due to an
absence of protective antibodies or other forms of immunity that older
individuals have gained over time.
A previous study at Rhode Island Hospital compared patients with pH1N1
to those infected with other respiratory viruses. While patients with
co-infections were excluded from the initial study, the current analysis
focused on this patient population, and hypothesized that those with
both pH1N1 and a respiratory virus would have worse outcomes than those
with just one infection.
However, Mermel and his colleagues found that despite the risk for
complications including treatment for a bacterial pneumonia,
co-infection was, in fact, not associated with worse outcomes.
“Although by our measures there was no demonstration of worse outcomes,
co-infected patients demonstrated a significant greater rate of patterns
of viral pneumonia by chest radiographs,” said principal investigator
Ignacio A. Echenique, M.D., a former Rhode Island Hospital researcher
who is now affiliated with Northwestern University. “These forms of
pneumonia would not be expected to respond to antibiotics. Ultimately,
the significance of the association of a co-infection with viral
pneumonias is unclear. While hospitalized patients with respiratory
virus co-infection did not experience poorer outcomes, our findings do
not address whether co-infection is a risk factor for hospitalization
The researchers concluded that a large, multi-center study should be
conducted across various levels of care to measure the impact of
co-infections on hospitalization, and to distinguish between viral and
bacterial pneumonia in co-infected patients.
The unfunded study was conducted
by Leonard Mermel, DO, ScM, Rhode Island Hospital and Alpert Medical
School; Ignacio A. Echenique, MD, Northwestern University in Chicago,
IL; Philip A. Chan, MD, MS, and Kimberle C. Chapin, MD, Rhode Island
Hospital and the Alpert Medical School; Sarah B. Andrea, BS, Rhode
Island Hospital; and Joseph Fava, PhD, The Miriam Hospital.