Biomedical Engineering Reference
In-Depth Information
(21,22). Greenberg et al. (23) studied viral etiologies of COPD exacer-
bations and found using viral culture and serology that 27% of COPD
exacerbations were associated with respiratory viruses, while in 44% of acute
respiratory illnesses in control subjects were associated with viruses. In the
COPD patients, rhinoviruses accounted for 43% of the virus infections
and thus responsible for about 12% of exacerbations. The advent of PCR
techniques for viral detection enabled a more detailed evaluation of the role
of viruses at asthmatic and COPD exacerbations. Studies in childhood
asthma have shown that rhinovirus can be detected by polymerase chain
reaction from a large number of these exacerbations (20).
Seemungal et al. (8) performed a study taking samples of nasophrayn-
geal aspirates or throat swabs at exacerbation and also when patients were
stable. Up to 40% of COPD exacerbations were associated with viral infec-
tions, though this may be an underestimate due to difficulties in sampling at
the very onset of an exacerbation. Rhinovirus was the commonest respira-
tory virus detected and found in 58% of viral exacerbations. The other
viruses detected included coronavirus (11% of virus exacerbations), influ-
enza A and B (8), Parainfluenza, Adenovirus, and Chlamydia pneumoniae
were each detected in one exacerbation. The relatively low levels of influenza
were related to the fact that 74% of the patients had received influenza
immunization. In another study of viruses at COPD exacerbations in
patients admitted to hospital, respiratory viruses were detected by PCR in
56% of exacerbations and again rhinovirus was the commonest virus to
be detected (24). Seemungal et al. (8) also showed that respiratory viruses
were associated with a longer median symptom recovery time at exacerba-
tion compared to the recovery time for nonviral exacerbations. (Fig. 4).
Thus, viruses are associated with more severe exacerbations and therefore
with greater morbidity. Measures to prevent viral infection may lead
to a reduction in exacerbation frequency, exacerbations severity, and
reduction in hospital admission and thus have important health economic
consequences.
Using the median number of exacerbations as a cut-off point, we have
previously classified COPD patients as frequent and infrequent exacerbators
(1). Quality of life was significantly worse in the frequent, compared to the
infrequent exacerbators. Factors predictive of frequent exacerbations
included the exacerbation frequency in the previous year. This suggests that
exacerbation frequency is an important determinant of health status in
COPD and is thus one of the important outcome measure in COPD. In
our study of Seemungal et al. (8) of respiratory virus detection by PCR,
at least one virus was detected in 64% of patients and these patients had a
higher exacerbation frequency than patients where viruses were not
detected. Thus, patients with a history of frequent exacerbations may be
more susceptible to respiratory viral infections and further work is required
to study the nature of this susceptibility.
