TABLE 3

Characteristics of Varicella Outbreaks and Outbreak-Related Cases in an Active Surveillance Site by 4-Year Time Periods, AV (CA), 1995–2010

Characteristic1995–19981999–20022003–20062007–2010Pa
Total number of outbreaks236524712<.01b
Duration of outbreak, median (range), d45 (7–198)41 (1–149)30 (3–72)38 (5–61)<.01
Outbreak-related cases
 Total number5409703499102<.01c
 Proportion of outbreak-related cases among total number of reported cases57.827.627.612.9<.01
Number of cases per outbreak, median (range)15 (5–124)11 (5–56)9 (5–45)9 (5–11)<.01c
Outbreak size, n (%) of outbreaks
 <10 cases65 (27.5)24 (46.2)30 (63.8)7 (58.3)<.01
 10–24 cases106 (44.9)22 (42.3)15 (31.9)5 (41.7)<.01
 25–49 cases39 (16.5)5 (9.6)2 (4.3)0<.01
 ≥50 cases26 (11.0)1 (1.9)00<.01
Age of case patients, median (range), y6 (0–59)7 (0–49)9 (0–43)11 (0–41)<.01c
Total outbreak case patients, by age, n (%), y
 <1150 (2.8)20 (2.8)5 (1.0)1 (1.0)<.01
 1–41596 (29.5)115 (16.4)25 (5.0)3 (2.9)<.01
 5–92987 (55.2)442 (62.9)254 (50.9)32 (31.4)<.01
 10–14402 (7.4)107 (15.2)194 (38.9)61 (59.8)<.01
 15–1973 (1.4)3 (0.4)10 (2.0)3 (2.9)<.01
 ≥20201 (3.7)16 (2.3)11 (2.2)2 (2.0)<.01
Vaccinated outbreak case patients, by age, n (%), y
 1–432 (2.0)38 (33.0)16 (64.0)1 (33.3)<.01
 5–940 (1.0)95 (21.5)201 (79.1)29 (90.6)<.01
 10–14 y1 (0.2)17 (15.9)73 (37.6)36 (59.0)<.01
 15–19 y0 (0)1 (33.3)2 (20.0)0NS
 ≥20 y6 (3.0)1 (6.3)2 (18.2)0NS
 Total79 (1.5)152 (21.6)294 (58.9)66 (64.7)<.01
Lesion count, n (%) of cases
 <501894 (35.0)287 (40.9)252 (51.0)59 (58.4)<.01
 ≥503515 (65.0)414 (59.1)242 (49.0)42 (41.6)<.01
Complications, n (%) of cases502 (9.3)39 (5.6)14 (2.8)1 (1.0)<.01
  • NS, not significant.

  • a Determined by χ2 test for trend, unless otherwise specified.

  • b Linear regression used to determine P value.

  • c Kruskal-Wallis test.