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. 2021 Aug 19;73(10):1759–1767. doi: 10.1093/cid/ciab709

Table 1.

Demographic and Clinical Characteristics of Study Participants by Case Status

Cases vs Controls
Characteristic Total (N = 1024) Cases (N = 512) Controls (N = 512) P Valuea
Demographics
  Hospital Hospital 1 523 (51.1) 252 (49.2) 271 (52.9) .260
Hospital 2 501 (48.9) 260 (50.8) 241 (47.1)
  Age at presentation, y Median 5.9 5.8 6 .981
IQR 2.7–10.3 2.7–10.2 2.6–10.4
  Age group, y 0 to <5 438 (42.8) 219 (42.8) 219 (42.8) .945
5 to <9 272 (26.6) 138 (27.0) 134 (26.2)
9+ 314 (30.7) 155 (30.3) 159 (31.1)
  Sex Female 497 (48.5) 242 (47.3) 255 (49.8) .453
Male 527 (51.5) 270 (52.7) 257 (50.2)
  Race/Ethnicity Hispanic 175 (17.1) 92 (18.0) 83 (16.2) <.001
Non-Hispanic Black 567 (55.4) 311 (60.7) 256 (50.0)
Non-Hispanic White 212 (20.7) 78 (15.2) 134 (26.2)
Otherb 70 (6.8) 31 (6.1) 39 (7.6)
  Season 2012–2013 266 (26.0) 133 (26.0) 133 (26.0) >.999
2013–2014 118 (11.5) 59 (11.5) 59 (11.5)
2014–2015 252 (24.6) 126 (24.6) 126 (24.6)
2015–2016 148 (14.5) 74 (14.5) 74 (14.5)
2016–2017 240 (23.4) 120 (23.4) 120 (23.4)
Vaccination
  Type Inactivated influenza vaccine 347 (33.9) 137 (26.8) 210 (41.0) <.001
Live attenuated influenza vaccine 23 (2.2) 12 (2.3) 11 (2.1)
None 654 (63.9) 363 (70.9) 291 (56.8)
   Advisory Committee on Immunization Practices vaccination status Complete 145 (14.2) 54 (10.5) 91 (17.8) <.001
Partial 225 (22.0) 95 (18.6) 130 (25.4)
None 654 (63.9) 363 (70.9) 291 (56.8)
Medical history
  Blood disorder Yes 169 (16.5) 94 (18.4) 75 (14.6) .130
  Cardiac disorder Yes 85 (8.3) 34 (6.6) 51 (10.0) .069
  Endocrine disorder Yes 31 (3.0) 14 (2.7) 17 (3.3) .716
  Immunocompromised Yes 134 (13.1) 69 (13.5) 65 (12.7) .781
  Kidney disorder Yes 29 (2.8) 17 (3.3) 12 (2.3) .452
  Liver disorder Yes 19 (1.9) 11 (2.1) 8 (1.6) .644
  Hematologic malignancy Yes 31 (3.0) 14 (2.7) 17 (3.3) .716
  Solid organ malignancy Yes 21 (2.1) 6 (1.2) 15 (2.9) .075
  Metabolic disorder Yes 16 (1.6) 6 (1.2) 10 (2.0) .451
  Neurologic disorder Yes 243 (23.7) 111 (21.7) 132 (25.8) .142
  Prematurityc Yes 45 (22.1) 15 (14.6) 30 (29.7) .011
  Respiratory disorder Yes 463 (45.2) 216 (42.2) 247 (48.2) .060
  Rheumatologic disorder Yes 7 (0.7) 1 (0.2) 6 (1.2) .124
  Any medical history Yes 788 (77.0) 393 (76.8) 395 (77.1) .941
Clinical presentation
  Body mass index Median 16.6 16.8 16.5 .168
IQR 15.0–19.4 15.1–19.4 14.8–19.5
  Days from vaccination to symptom onset Median 85 86 84 .658
IQR 54.0–125.0 56.0–132.0 53.0–124.0
  Days of symptoms Median 3 3 3 .496
IQR 2.0–6.0 2.0–6.0 2.0–6.0
  Fever Yes 832 (81.3) 468 (91.4) 364 (71.1) <.001
  Days of feverd Median 2 2 2 .880
IQR 1.0–4.0 1.0–4.0 1.0–4.0
  Highest recorded temperature (ºC)d Median 39 39.1 38.9 .002
IQR 38.3–39.6 38.6–39.6 38.2–39.5
  >3 symptomse Yes 677 (66.1) 349 (68.2) 328 (64.1) .187
Microbiologyf
 Influenza A Positive 370 (36.1) 370 (72.3) 0 (0.0) <.001
  Influenza B Positive 143 (14.0) 143 (27.9) 0 (0.0) <.001
  Human metapneumovirus Positive 58 (5.7) 5 (1.0) 53 (10.4) <.001
  Adenovirus Positive 20 (2.0) 6 (1.2) 14 (2.7) .112
  Chlamydophila pneumoniae Positive 1 (0.2) 1 (0.3) 0 (0.0) >.999
  Coronavirus Coronavirus 229E Positive 7 (1.1) 4 (1.2) 3 (0.9) >.999
  Coronavirus HKU1 Positive 2 (0.3) 1 (0.3) 1 (0.3) >.999
  Coronavirus NL63 Positive 17 (1.7) 3 (0.6) 14 (2.7) .012
  Coronavirus OC43 Positive 15 (2.3) 4 (1.2) 11 (3.4) .114
  Mycoplasma pneumoniae Positive 6 (0.8) 2 (0.5) 4 (1.1) .686
  Parainfluenza 1 Positive 2 (0.2) 0 (0.0) 2 (0.4) .500
  Parainfluenza 2 Positive 2 (0.2) 0 (0.0) 2 (0.4) .500
  Parainfluenza 3 Positive 6 (0.6) 3 (0.6) 3 (0.6) >.999
  Parainfluenza 4 Positive 3 (0.3) 0 (0.0) 3 (0.6) .249
  Rhinovirus/Enterovirus Positive 168 (16.4) 25 (4.9) 143 (27.9) <.001
  Respiratory syncytial virus Positive 99 (9.7) 15 (2.9) 84 (16.4) <.001
Antiviral use while hospitalized
  Oseltamivir Yes 452 (44.1) 447 (87.3) 5 (1.0) <.001
  Days of treatmentg Median 6 6 1 <.001
IQR 5.0–6.0 5.0–6.0 1.0–1.0
Outcome
  Days of hospitalization Median 4 3 4 <.001
IQR 3–5 3–5 3–6
  Intensive care unit admission Yes 340 (33.2) 139 (27.1) 201 (39.3) <.001
  Mechanical ventilation Yes 67 (6.5) 28 (5.5) 39 (7.6) .206
  Radiographic pneumoniah Yes 228 (22.3) 123 (24.0) 105 (20.5) .202

Abbreviations: HMPV, human metapneumovirus; IQR, interquartile range.

aCases and controls compared using the Fisher exact test for categorical variables and Wilcoxon rank sum test for continuous variables.

bOther races included American Indian/Alaska Native, Asian, Native Hawaiian or Other Pacific Islander, multiple races, and unknown.

cPrematurity history unavailable for participants aged >2 years at admission.

dDays of fever and maximum temperature only defined for participants with fever.

eParticipants may be missing data for 1 or multiple symptoms.

fMicrobiology notes: One case coinfected with influenza A and B. A total of 101 participants were positive for multiple pathogens, with a maximum of 3 pathogens identified. Coronavirus Coronavirus 229E, coronavirus HKU1, and coronavirus OC43 results were missing in 378 participants (189 cases, 189 controls). Chlamydophila pneumoniae results were missing in 375 participants (187 cases, 188 controls), and Mycoplasma pneumoniae results were missing in 265 participants (133 cases, 132 controls).

gDays of treatment only defined for participants who received treatment.

hRadiographic pneumonia identified by presence of International Classification of Diseases, Ninth Revision, Clinical Modification and International Classification of Diseases, Tenth Revision, Clinical Modification, code.