Pertussis
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þ Clinical Features of Pertussis (Whooping Cough)
 - only 44% have a typical "whoop" (single stridorous inspiration after
   coughing episode)
 - commonest finding in those under age 6 months was periodic apnea.
   [Gordon M. Clinical and microbiological features of children presenting
   with pertussis to a Canadian pediatric hospital during an eleven year
   period. Pediatr Infect Dis Journal 1994;13:617-622.]