Table 4.

Social risk factors and primary transmission settings and contributing factors for large outbreaks of tuberculosis detected in the United States during 2014–2016^a.

	Social risk factors			Primary setting of transmission				Contributors to transmission
Outbreak ID	Percent reporting homelessness in past year	Percent incarcerated at diagnosis	Percent reporting substance use in past yearb	Residentialc		Congregated		Source case with prolonged infectious periode	Difficulty in eliciting contacts	Barriers to accessing healthcare
				Family	Social	Overnight	Other
1	0.0	0.0	5.9	✓				✓
2	50.0	3.9	23.1			✓			✓	✓
3	5.3	0.0	0.0	✓				✓	✓	✓
4	30.0	13.3	50.0	✓				✓
5	10.5	15.8	26.3		✓				✓
6	19.4	3.2	35.5		✓			✓	✓
7	15.0	0.0	95.0		✓				✓	✓
8	3.9	0.0	15.4		✓				✓
9	6.7	73.3	35.6			✓
10	0.0	0.0	5.6				✓		✓	✓
11	0.0	0.0	0.0				✓	✓
12	4.0	0.0	4.0	✓				✓
13	0.0	0.0	0.0	✓				✓
14	13.2	5.3	29.0			✓
15	0.0	87.5	0.0			✓		✓
16	0.0	0.0	19.1		✓				✓	✓
17	50.0	6.3	75.0			✓			✓
18 f	9.1	0.0	36.4
19	0.0	0.0	27.3	✓						✓
20	0.0	0.0	42.9	✓				✓		✓
21	0.0	0.0	0.0				✓	✓
22	13.3	0.0	60.0		✓				✓
23	41.2	5.9	58.8		✓				✓
24	10.0	5.0	45.0		✓			✓	✓
Total a	6.0 (0–50)	0.0 (0–87.5)	26.8 (0–95)	7 (30.4%)	8 (34.8%)	5 (21.7%)	3 (13.0%)	11 (47.8%)	12 (52.2%)	7 (30.4%)

^aLarge outbreaks detected during 2014–2016 might include cases reported during 2010–2018 because the surveillance time periods extend before and after the date of first detection. In collaboration with state health departments, we qualitatively summarized the primary transmission settings and contributing factors for each large outbreak. These data were based on local knowledge and investigations (sometimes with CDC onsite assistance) of the outbreaks. We categorized the outbreaks based on the primary transmission settings and contributing factors that health departments identified for the entire outbreak. A blank for any of these fields indicates that the information is either unknown or was not identified as a primary setting or contributor to transmission for the outbreak. Values shown represent the median (range) for social risk factors and no. (%) for primary settings and contributors to transmission. Outbreak investigations were conducted for 23 of the 24 large outbreaks; percentages are calculated using 23 as the denominator.

^bSubstance use is defined as any self-reported use of alcohol to excess or any use of illicit drugs within the year before diagnosis.

^cOutbreaks in residential settings were classified as either transmission primarily within families or transmission primarily among nonfamilial social contacts. Some degree of transmission within families is expected for most residential outbreaks, so we only classified outbreaks as such if the health department reported that transmission primarily occurred within families.

^dOvernight congregate settings were defined as facilities where infection control measures for occupants staying overnight would be recommended by public health authorities, such as correctional facilities, overnight homeless shelters, hospitals, and long-term care facilities. Other congregate settings, which typically lack such measures, include schools, places of worship, workplaces, restaurants/cafés, bars, and casinos.

^eA source case with a long infectious period is defined as an individual who the health department reported was the apparent source leading to most or all of the secondary cases in the outbreak.

^fAn investigation was not conducted for this outbreak, so the primary settings and drivers of transmission were not known.