John W. Williams, Jr., MD and David L. Simel, MD
1 July 1993 | Volume 119 Issue 1 | Page 92
Drs. Cass, Cantor, and Clover's first concern is the generalizability
of the study results. Although the study site is university affiliated,
it serves as the primary care site (not tertiary care) for a population
of primarily local residents. We agree that the study population
was atypical in that only men were included; however, no known gender
differences exist in the clinical presentation or clinical course
Their second concern is the high prevalence of sinusitis (38%)
and possible misclassification by the criterion standard radiographs.
The epidemiologic data Cass and colleagues use to suggest a lower
prevalence of sinusitis is suspect because diagnoses were made without
objective clinical criteria or criterion standard confirmation.
Incidence data on complications of common colds should not be extrapolated
to the prevalence of sinusitis in symptomatic patients whose antecedents
include allergic rhinitis, upper respiratory tract infections, and
anatomic defects. Nevertheless, we too were surprised by the high
prevalence. Few quality data on sinusitis in general medical practice
exist; however, studies in subspecialty populations [1,2] and in
British general practices  showed an even higher prevalence in
symptomatic patients. We suggest that the 0.5% incidence rate has
been misinterpreted and that the prevalence of sinusitis in patients
meeting entry criteria for our study is indeed high.
Cass and colleagues' third concern is that roentgenogram misclassification
may have been increased by including patients with chronic sinusitis,
which by definition includes patients with symptoms lasting longer
than 3 months ; these patients were excluded from our study.
Compared with sinus aspiration and culture, radiographs do misclassify
a small proportion of patients. However, repeat radiographs 3 to
6 weeks later might not decrease the misclassification rate because
information about the relative time course for radiographic resolution
of acute sinusitis is incomplete.
We agree wholeheartedly that independently validated results yield
much greater confidence. However, given the sample size and number
of clinical variables, split sample training and validation sets
were not feasible. We elected not to use bootstrap or jackknife
validation methods; instead we continue to collect data to validate
our prospective findings.
University of Texas Health Science Center; San Antonio, TX 78284
Duke University; Durham, NC 27705
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