Background
Pertussis has three stages: Catarrhal stage > Paroxysmal stage > Convalescent stage (2-3 weeks).
Causative agent: Bordetella pertussis
Diagnosis
H&P
Risk factors:
Common presentation:
DDx
Diagnostic studies: The CDC recommends both a nasopharyngeal culture and polymerase chain reaction (PCR) testing to confirm the diagnosis.
Serologic testing is useful only in research settings.
Treatment
Azithromycin or Clarithromycin should be used as initial therapy. This is to decrease transmission pertussis to others and does not usually improve symptoms.
Start treatment within 6 weeks of onset of the cough in patients younger than 12 months and within 3 weeks in all other patients.
Trimethoprim/sulfamethoxazole is an alternative in cases of allergy or intolerance to macrolides.

Reference

http://www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html

Am Fam Physician 2013;88(8):507-514.

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