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. Author manuscript; available in PMC: 2020 May 6.
Published in final edited form as: Clin Infect Dis. 2015 Jun 25;61(9):1421–1431. doi: 10.1093/cid/civ514

Table 5.

Attack Rates of Coprimary and Secondary Cough Illnesses Among Household Members of Patients With Parapertussis, by Receipt of Azithromycin Prophylaxis and Age of Household Members—Wisconsin, 1 October 2011–31 May 2012

Azithromycin Prophylaxis Received
Household Member Age Category Household Members No. Cough Illness Type Occurring Among Household Members Yes No
No. Attack Rate (%) No. Attack Rate (%) P Valuea
All ages 478 131 347
Coprimaryb 1/131 (1) 39/347 (11) <.001
Secondaryc 0/130 (0) 36/308 (12) <.001
Aged >10 y 317 90 227
Coprimaryb 1/90 (1) 8/227 (4) .45
Secondaryc 0/89 (0) 14/219 (6) .013
Aged 1–10 y 149 36 113
Coprimaryb 0/36 (0) 29/113 (26) <.001
Secondaryc 0/36 (0) 20/84 (24) <.001
Aged <1 y 12 5 7
Coprimaryb 0/5 (0) 2/7 (29) .470
Secondaryc 0/5 (0) 2/5 (40) .444

The primary patient in each household was excluded from these analyses.

a

P-value of Fisher exact test for difference in attack rate by receipt of azithromycin prophylaxis.

b

Coprimary illness is defined as cough onset 0–6 days after cough onset in the household primary patient.

c

Secondary illness is defined as cough onset 7–16 days after cough onset in the household primary patient. Attack rate calculations exclude from the denominator all persons with coprimary illnesses because persons with coprimary illnesses were not at risk for having a secondary illness.