Table 1.

Characteristics of the 1665 contacts involved in the outbreak^a

Variables	Acquired TB (n = 22)b	Did not acquire TB (n = 1643)	P value
	No. (%)	No. (%)
Age (y), median (min, max)	20.0 (15.9‐39.8)	21.8 (2.4‐94.0)	.441
<15	0 (0)	14 (0.9)
16‐25	21 (95.5)	1227 (74.7)
26‐35	0 (0)	120 (7.3)
36‐45	1 (4.6)	73 (4.4)
46‐55	0 (0)	129 (7.9)
56‐65	0 (0)	62 (3.8)
≥65	0 (0)	18 (1.1)
Sex
Male	8 (33.4)	855 (52.0)	.144
Female	14 (66.7)	788 (47.9)
Source patient sputum smear results
Negative or scanty	0 (0.0)	630 (38.3)	<.0001
Positive	22 (100.0)	1013 (61.7)
Context of contacts
University contacts	19 (86.4)	984 (60.0)	.031
Household contactsc	2 (9.5)	94 (5.7)
Private tutoring class	1 (4.8)	213 (13.0)
Contacts in other settingsd	0 (0)	352 (21.4)
Contacts of the index case
No	3 (13.6)	1522 (92.6)	<.0001
Yes	19 (86.4)	121 (7.4)
Isoniazid preventive therapy
No	22 (100.0)	1470 (89.5)	.158
Yes	0 (0)	173 (10.5)
Contact under CO2 level >1000 ppme
No	1 (4.6)f	722 (43.9)	<.0001
Yes	21 (95.5)	921 (56.1)

P value, by chi‐square test or Fisher's exact test (if the sample size is smaller than five).

Abbreviations: CO₂, carbon dioxide; ppm, parts per million; TB, tuberculosis.

^aAll student, staff, and faculty with a cumulative 30‐40 h exposure to shared air (defined as staying in the same floor or within the same building with any infectious TB patient) were considered as contacts. Public health nurses used administrative data (lists of students/faculties/employee, curriculum, and class rosters) and results from a structured questionnaire to identify contacts as many as possible. Initially, 40 h were used. However, one contact with 30 h exposure to the index case became Case 3. Thereafter, the authority updated the operative definition for university contacts to a cumulative 30 h exposure to shared air, due to the severely underventilated environment in University A.

^bThe total 27 TB cases in this outbreak include the index case (Case 0), twenty‐two contacts who acquired active TB during follow‐up, and four additional TB cases who had exposure to shared air with infectious TB cases but did not meet the operative definition of contact (see the legend of Figure 3).

^cThree household contacts were also university contacts (one is the index case's sister, who acquired active TB, and two are Case 5's roommates who attended the same school).

^dFriends (n = 19), workplace contacts (n = 165), flight contacts (n = 3), contacts at another university (n = 165).

^eDefined as having an indoor air CO₂ level >1000 ppm at the time of exposure. Contacts in this category include the 728 university contacts who were exposed to TB patients in this outbreak before the ventilation engineering was completed on January 16, 2012. One TB patient (Case 8) attended a private tutoring class. Public health inspectors found the tutoring class had a CO₂ level of 1022 ppm. Therefore, the 214 tutoring class attendees were also considered to have been exposed to TB patients in environment with a CO₂ level >1000 ppm.

^fThis is a household contact.