Table 2.

Study Characteristics for 129 Included Studies

	N (%)
Study design
Prospective cohort	41 (31.8)
Retrospective cohort	34 (26.4)
Case/control	17 (13.2)
Disease burden/models/surveillance estimates	15 (11.6)
Systematic review or meta-analysis	11 (8.5)
Review	2 (1.6)
Economic Estimates	2 (1.6)
Nested case/control	1 (0.8)
Cross-sectional	1 (0.8)
Other	5 (3.9)
Case population source
Routine surveillance	48 (37.2)
Outbreak	39 (30.2)
Specialty clinic	9 (7.0)
Chart review	6 (4.7)
Other (population registry, military health encounters, multiple sources)	27 (20.9)
Years of study
Range	1960–2016
Length of study (n = 58, excluding 9 studies more than 5 years long)
Mean, months	19.1
Range, months	1–60
Region of World (multiple select)
Europe	65
United States	26
Australia and New Zealand	8
Systematic review	11
Other**	24
Percentage of cases male (n = 83 studies)
Mean	46.4
Range	5–99.4

Counts for cases and controls were collected but missing for 38 (number of cases) and 81 (age range); this information was excluded from this table due to missingness.

^**Other countries included: Canada (n = 7), South Korea (n = 4), India (n = 2), Mexico (n = 2), Chile (n = 1), China (n = 1), Israel (n = 1), and multiple (n = 6).