We categorized patients into the acute epglottitis (case) group and the non-epiglottitis (control) group. Patients who met the following criteria were selected into the case group: (1) diagnosed with acute epiglottitis based on the ICD-9-CM codes 464.3, 464.30, or 464.31 by an otolaryngologist; (2) two or more ambulatory visits or at least one inpatient visit for acute epiglottitis; and (3) no concomitant deep neck infection—that is, ICD-9 codes 528.3 (cellulitis and abscess of oral soft tissues), 478.22 (parapharyngeal abscess), 478.24 (retropharyngeal abscess), or 682.11 (cellulitis and abscess of neck). For each of these patients, the date of initial epiglottitis diagnosis was assigned as the index date. To increase statistical power, for each case identified on the index date, we randomly selected four subjects without acute epiglottitis as controls on the same day. Both cases and controls were identified from the LHID 2005 with records between January 1, 2000, and December 31, 2013. The groups were frequency matched for sex, age, urbanization leveland income.
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