TABLE 1

Demographic and Clinical Characteristics of the Study Population, Overall and Stratified by Chronic Condition Status and Antibiotic Use

CharacteristicNo Antibiotics at 0–<24 moYes Antibiotics at 0–<24 mo
No Complex Chronic Condition, N = 130 208With Complex Chronic Conditiona, N = 23 158No Complex Chronic Condition, N = 180 739With Complex Chronic Conditiona, N = 28 445
Female sex, n (%)65 260 (50)10 693 (46)85 289 (47)12 666 (45)
Race, n (%)
 Asian American5978 (5)750 (3)6994 (4)791 (3)
 African American36 268 (28)4682 (20)48 936 (27)7915 (28)
 White65 597 (50)13 609 (59)96 217 (53)15 389 (54)
 Other9778 (8)2808 (12)12 499 (7)2767 (10)
 Unknown12 587 (10)1309 (6)16 093 (9)1583 (6)
Hispanic ethnicity, n (%)26 757 (21)3577 (15)29 498 (16)4187 (15)
Pretermb, n (%)6977 (5)3513 (15)10 002 (6)5527 (19)
Asthmac, n (%)10 596 (8)2577 (11)27 750 (15)6673 (23)
Systemic corticosteroid episodesd at <24 mo of age, n (%)
 0123 892 (95)21 663 (94)147 406 (82)21 434 (75)
 15024 (4)1006 (4)22 408 (12)3776 (13)
 2845 (1)264 (1)6447 (4)1491 (5)
 3259 (0)114 (0)2430 (1)741 (3)
 4+188 (0)111 (0)2048 (1)1003 (4)
Episodes for presumed infectious illnessese at <24 mo of age, n (%)
 029 480 (23)5005 (22)11 341 (6)846 (3)
 118 363 (14)2830 (12)5989 (3)805 (3)
 218 571 (14)2486 (11)10 715 (6)1117 (4)
 316 273 (12)2132 (9)14 723 (8)1477 (5)
 4+47 521 (36)10 705 (46)137 971 (76)24 200 (85)
No. encountersf at <24 mo of age, median (IQR)12.0 (7.0 to 16.0)17.0 (9.0 to 28.0)19.0 (13.0 to 26.0)29.0 (18.0 to 47.0)
Systemic antibiotic prescribing episodesg at <24 mo of age, n (%)
 0130 208 (100)23 158 (100)
 167 287 (37)9965 (35)
 240 199 (22)6034 (21)
 325 202 (14)3804 (13)
 4+48 051 (27)8642 (30)
Systemic broad-spectrum antibiotic prescribing episodesg at <24 mo of age, n (%)
 0130 208 (100)23 158 (100)73 520 (41)8138 (29)
 153 513 (30)8917 (31)
 222 637 (13)4219 (15)
 312 114 (7)2468 (9)
 4+18 955 (10)4703 (17)
Systemic narrow- spectrum antibiotic prescribing episodesg at <24 mo of age, n (%)
 0130 208 (100)23 158 (100)29 521 (16)9152 (32)
 179 035 (44)10 222 (36)
 240 332 (22)4668 (16)
 318 903 (10)2249 (8)
 4+12 948 (7)2154 (8)
BMI category at 48–<72 mo of age, n (%)
 Underweight (less than the fifth percentile)6062 (5)1770 (8)6798 (4)1680 (6)
 Normal wt (fifth to <85th percentile)89 441 (69)14 926 (64)122 554 (68)18 321 (64)
 Overweight (85th to <95th percentile)18 070 (14)3247 (14)27 225 (15)4232 (15)
 Obese (≥95th percentile)16 635 (13)3215 (14)24 162 (13)4212 (15)
Age, mo (SD)57.8 (5.5)57.9 (5.0)57.8 (5.3)58.1 (4.7)
BMI z score (SD)0.36 (1.19)0.30 (1.32)0.44 (1.15)0.39 (1.27)
  • IQR, interquartile range; —, not applicable.

  • a Defined as ≥2 ICD-9-CM codes for a complex chronic condition at <72 months of age on the basis of a previously published code set.

  • b One or more ICD-9-CM codes for prematurity at <24 months of age.

  • c Two or more ICD-9-CM codes for asthma at <72 months of age.

  • d Multiple corticosteroids given on the same day or within 10 days of each other were considered a single prescribing episode.

  • e Defined by ICD-9-CM codes on the basis of Fleming-Dutra et al.35

  • f Included all encounters in the inpatient, emergency department, urgent care, and outpatient settings.

  • g Multiple antibiotics given on the same day or within 10 days of each other were considered a single prescribing episode; 91.6% of episodes included a prescription written on a single day, with 99.6% of episodes spanning ≤30 days.