Table 1. Baseline Characteristics of the Study Population at the Index Date With 15 Days of Window Perioda.
| Variable | Participants, No. % (nā=ā3178) |
|---|---|
| Age at the index dateb | |
| 6-24 mo | 985 (31.0) |
| 25 mo to 6 y | 1445 (45.5) |
| ā„7 y | 748 (23.5) |
| Sex | |
| Boys | 1776 (55.9) |
| Girls | 1402 (44.1) |
| Region of birthc | |
| Seoul | 1095 (34.5) |
| Metropolitan | 487 (15.3) |
| Urban | 1319 (41.5) |
| Rural | 233 (7.3) |
| Economic statusd | |
| Low (<25th percentile) | 687 (21.6) |
| Intermediate (25th to 75th percentile) | 1826 (57.5) |
| High (>75th percentile) | 604 (19.0) |
| Calendar year at birth | |
| 2002 | 659 (20.7) |
| 2003 | 758 (23.9) |
| 2004 | 863 (27.2) |
| 2005 | 898 (28.3) |
| Clinical conditions | |
| Admission to intensive care unit before age 6 mo | 101 (3.2) |
| Any perinatal condition | 950 (29.9) |
| Length of gestation and fetal growth | 84 (2.6) |
| Convulsion, CNS disturbance | 38 (1.2) |
| Congenital malformation | 703 (22.1) |
| Chromosomal anomaly | 50 (1.6) |
| Birth trauma | 14 (0.4) |
| Respiratory and cardiovascular disorder | 97 (3.1) |
| Infection specific to the perinatal period | 242 (7.6) |
| No. of perinatal conditions | |
| 0 | 2228 (70.1) |
| 1 | 714 (22.5) |
| 2 | 155 (4.9) |
| ā„3 | 81 (2.5) |
Abbreviation: CNS, central nervous system.
a
The final study population included participants with a 15-day window who had been prescribed antihistamines during either the hazard or control periods.
b
The index date was defined as the date of the seizure event. The seizure event was defined as an emergency department visit with a principal diagnosis of epilepsy (International Statistical Classification of Diseases and Related Health Problems, Tenth Revision [ICD-10], code G40.X), status epilepticus (ICD-10 code G41.X), or convulsion (ICD-10 code R56.8).
c
Owing to missing data for 44 participants (1.4%), percentages do not total 100.
d
Owing to missing data for 61 participants (1.9%), percentages do not total 100.