Without a doubt, 2009 was an extraordinary year from
the respiratory virus testing perspective. A relatively unremarkable,
mild flu season began the year and then, in spring, swine flu, as it was
called then, struck. The reported numbers of cases rose from day to day
in those early weeks of the outbreak. The general public panicked,
governments mobilized, and the rush for a vaccine began. The virus
officially became 2009 Influenza A/H1N1. Cases around the world were
monitored as the numbers of sick rose and fell through the summer, fall
and winter. In labs, some institutions were overwhelmed by the sheer
volume of samples they received.
As the 2009 Influenza A/H1N1 pandemic wanes, we have
the opportunity to look back at what the last year taught about
influenza and the testing methods commonly employed to help diagnose and
track the spread of such pathogens. The symptoms of respiratory viruses
are so similar that they are nearly impossible to distinguish, and
misdiagnosis of influenza based on symptoms alone is common. A 2006
study found that less than 30% of children were correctly diagnosed with
influenza based on clinical assessment alone.1
During the 2009 pandemic, Children’s Hospital of
Philadelphia saw firsthand how easy it is to mistake influenza for
another respiratory virus. The hospital saw a spike in patients with
influenza-like symptoms. At first, officials believed the spike in
illnesses was due to 2009 Influenza A/H1N1, but lab results revealed
many of the cases were caused by rhinovirus.2
The importance of distinguishing those with influenza
from those who do not have it is further demonstrated by data from the
Centers for Disease Control and Prevention (CDC). At the height of the
pandemic, no more than 42% of samples tested for influenza by CDC labs
were positive for the pathogen. Misdiagnosis can mean unnecessary or
incorrect use of antivirals or antibiotics, and can lead to unneeded
medical procedures and tests. Laboratory testing is essential for an
accurate diagnosis.
While many types of tests were employed in lab during
the 2009 Influenza A/H1N1 pandemic, multiplexed molecular assays emerged
as important tools. Comprehensive, fast, and accurate, these assays
proved to be cost-effective and assisted a number of lab in saving
valuable time and resources as the pressure to process more patient
samples increased.
Multiplexed molecular assays have many advantages in
contrast to other methods, are sensitive and specific, and can
accurately identify a broad range of respiratory viruses. These tests,
which are typically PCR-based, also can detect co-infections from a
single patient sample. Most multiplexed molecular tests can provide
results within 24 hours.
A study conducted during the 2009 Influenza A/H1N1
outbreak in the New York City area evaluated the performance of several
different influenza A testing methods, finding that multiplexed tests
provided the best diagnostic option in respiratory testing due to high
sensitivity for the detection of all influenza strains, including the
2009 Influenza A/H1N1. In the study, more than 6,000 patient samples
were submitted over a five-week period for a total of 14,114 viral
diagnostic tests performed. Testing methods used included rapid antigen,
direct immunofluorescent antibody (DFA), viral culture, and PCR. Before
the study was conducted, little was known about the performance of these
tests for the detection of 2009 Influenza A/H1N1 in the context of
seasonal H1N1, H3N2, and other circulating respiratory viruses. The
tests needed to be able to subtype influenza A in order to identify
high-risk patients with 2009 Influenza A/H1N1 infection and to monitor
the spread of the outbreak.
The New York study found the rapid tests’
sensitivities were 10.4% and 9.6% for the detection of both seasonal
influenza A and novel H1N1, respectively. A particular brand of rapid
test yielded better sensitivity results of seasonal influenza A (41.2%)
and 2009 Influenza A/H1N1 (40%). The sensitivity of DFA tests was
slightly higher for influenza A (48.6%) and 2009 Influenza A/H1N1
(46.7%). The multiplexed PCR-based tests detected 97.8% of both
influenza A and 2009 Influenza A/H1N1 cases. The PCR test’s specificity
was found to be 100% in both flu strains.3
A study in Canada performed a cost analysis comparing
PCR testing with other methods such as DFA and shell vial culture, and
looked at the charts of 661 pediatric patients to determine the length
of hospital stay, the number of days in isolation, antibiotic usage, and
all other medical procedures performed. After comparison, the least
costly strategy was found to be the multiplexed PCR test, indicating a
savings of $291 per case, resulting in a savings of $529,620 per year in
direct costs for the hospitals involved.4
As we look toward next flu season and new flu strains
it may bring, we should consider the lessons learned in 2009 about
respiratory virus testing and the important role that multiplexed
respiratory virus tests can play in assisting in disease diagnosis and
surveillance. Multiplexed tests have shown to offer many benefits to the
healthcare system, including improved patient care and health outcomes,
reduced healthcare costs, and enhanced efficiencies in healthcare
delivery and laboratory operations. These tests can provide
comprehensive, accurate results within 24 hours, giving us important
data about exactly what is infecting a particular patient and
circulating in our communities.
Nancy Krunic, PhD, is vice president of Luminex
Molecular Diagnostics in Toronto, Ontario, Canada.
References
- Poehling KA, et al. NEJM.
2006;355(1):31-40. - Sapatkin D. “Ill this fall? Maybe it wasn’t swine
flu after all,” Philadelphia Inquirer, Nov. 12, 2009.
http://www.philly.com/inquirer/health_science/daily/20091112_Tests_show_fall
_outbreak_is_rhinovirus__not_swine_flu.html .
Accessed February 22, 2010. - Ginocchio CC, et al. Evaluation of multiple test
methods for the detection of the novel 2009 influenza A (H1N1)
during the New York City outbreak. J Clin Virol.
2009;45:191-195. - Mahony JB, et al. Cost Analysis of Multiplex PCR
Testing for Diagnosing Respiratory Virus Infection.
J Clin Microbiol. 2009;47(9):2812-2817.
