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Table 2 Characteristics of medical and control enrollees, those who refused participation, and all other pregnant women at study sites during study year two (2011–12)

From: Factors associated with recruitment, surveillance participation, and retention in an observational study of pregnant women and influenza

 

A

B

A vs. B

C

A + B vs. C

D

A + B vs. D

Medical Enrollees

(Year 2) a

ARI-Negative Control Enrollees

(Year 2) a

Medical vs. Control Enrollees

Reached for Recruitment but Refused to Participate

Medical and Control Enrollees vs. Refused

All Other Pregnant Women During Study (Year 2) b

Enrollees vs. All Other Pregnant Women

Total N

151

103

 

514

 

19,264

 

Source: Medical Record, Categorical Variables, N (Col. %)

 Study Site

  

p < .0005

 

p < .0005

 

p < .0005

  Site 1

50 (33)

20 (19)

 

229 (45)

 

3466 (18)

 

  Site 2

101 (67)

83 (81)

 

285 (55)

 

15,798 (82)

 

 Race (White)

  

p = .01

 

p = .01

 

p < .0005

  White

81 (54)

39 (38)

 

309 (60)

 

11,213 (58)

 

  Non-White

79 (52)

64 (62)

 

178 (35)

 

7409 (38)

 

  Unknown Race

   

27 (5)

 

642 (3)

 

 Ethnicity

  

p = .045

 

NA c

 

NA c

  Hispanic/Latina

53 (35)

24 (23)

 

96 (19)

 

3684 (19)

 

  Non-Hispanic

98 (65)

79 (77)

 

147 (29)

 

7206 (37)

 

  Unknown Ethnicity

   

271 (53)

 

8374 (43)

 

 High Risk Medical Conditions

  Chronic Condition (prior to pregnancy)

37 (25)

12 (12)

p = .01

95 (18)

p = .27

2108 (11)

p = .03

  Pregnancy Complication

128 (85)

76 (74)

p = .03

380 (74)

p = .47

11,816 (61)

p = .001

 Medical visits for ARI (1 or more)

  Year Prior to Study (12 months)

39 (26)

24 (23)

p = .21

133 (26)

p = .67

2799 (15)

p < .0005

  During Study Period (6 months)

NA

NA

 

NA

 

NA

 

 Study Season’s Influenza Vaccination

79 (52)

65 (63)

p = .09

130 (25)

p = .008

7432 (39)

p = .17

Medical Record, Continuous, Mean (95% CI)

 Woman’s Age (at start of season), Years d

  Site 1

28.5 (26.8–29.5)

28.5 (26.8–29.5)

 

30.0 (29.2–30.7)

 

29.4 (29.1–20.5)

 

  Site 2

30.9 (230.1–31.7)

30.9 (230.1–31.7)

 

31.3 (30.7–32.0)

 

31.4 (31.3–31.5)

 

 Gestational Age (at start of season), Days d

  Site 1

105 (79–130)

105 (79–130)

 

123 (108–137)

 

146 (142–150)

 

  Site 2

97 (85–110)

97 (85–110)

 

91 (81–101)

 

105 (104–107)

 
  1. Abbreviations: NA Not applicable, ARI Acute respiratory illness; ICD-9-CM codes 460–466 and 480–488
  2. aMedical enrollees are women who were recruited by telephone following a medical visit for ARI; ARI-negative controls had no medical visit for ARI and had not self-reported illness with fever and cough since the start of the local influenza season
  3. bRecords for potential participants who could not be reached by telephone were not available for study year 2; therefore, “all other pregnant women during study” includes women we attempted to contact but never reached and the much larger population of pregnant women who were not selected as potential participants
  4. cWe did not calculate a statistical comparison for ethnicity for refusers and the full source population given the large number with unknown ethnicity in the medical records; the comparison of medical vs. ARI-negative control enrollees relied on self-reported ethnicity
  5. dWomen’s age and age of fetus were calculated using a common reference date, which was the start of the influenza season at each study site