. 2023 Aug 4;4(8):e232310. doi: 10.1001/jamahealthforum.2023.2310

Table 3. Secondary Transmission and Exposure Characteristics, Fall 2021 (Univariable Analysis).

Exposure	No. of students, faculty, and staff^a					SAR, %	Fisher exact P value
Exposure	Index cases	Contacts	Contacts tested	No in-school transmission	In-school transmission	SAR, %	Fisher exact P value
Contact role
Staff	37	107	107	107	0	0	.07
Student	207	1566	1487	1443	44	3.0	.07
Contact grade level and staff
Prekindergarten, kindergarten, and elementary^b	143	940	888	847	41	4.6	<.001
Middle school^c	44	381	374	372	2	0.5
High school^d	24	237	220	219	1	0.5
Staff	37	107	107	107	0	0
Not available	4	8	5	5	0	0
Classroom exposure
No	132	497	485	479	6	1.2	.01
Yes	187	1176	1109	1071	38	3.4	.01
Lunch exposure
No	207	1294	1218	1180	38	3.1	.15
Yes	106	379	376	370	6	1.6	.15
Sports exposure
No	214	1658	1580	1536	44	2.8	>.99
Yes	2	15	14	14	0	0	>.99
Distance during exposure, ft
<3	168	1214	1203	1174	29	2.4	.003
<6 (Not specified)	13	72	68	68	0	0
3-6	35	177	116	115	1	0.9
Unknown	37	210	207	193	14	6.8
Masking during exposure
Both case and contact masked	172	1042	970	948	22	2.3	.003
Case masked and contact unmasked	4	8	8	8	0	0
Neither masked	109	411	407	400	7	1.7
Unknown	33	212	209	194	15	7.2
Quarantine/testing approach
TTS	186	1110	1110	1079	31	2.8	<.001
Quarantine	36	73	64	58	6	9.4
Vaccinated; tested on day 3-5	55	350	350	350	0	0
Other	19	77	10	9	1	10.0
Contact vaccination status
Fully vaccinated	65	410	398	398	0	0	<.001
Partially vaccinated	22	66	57	54	3	5.3
Unvaccinated	194	1183	1128	1087	41	3.6
Index case role
Staff	21	200	162	161	1	0.6	.12
Student	194	1473	1432	1389	43	3.0	.12
Index case grade level and staff
Prekindergarten, kindergarten, and elementary^b	131	869	843	804	39	4.6	<.001
Middle school^c	42	388	379	376	3	0.8
High school^d	21	216	210	209	1	0.5
Staff	21	200	162	161	1	0.6
Means of identifying index case
In-school close contact, enrolled in TTS program	7	52	52	51	1	1.9	.55
In-school close contact, not enrolled in TTS program	1	2	2	2	0	0
Out-of-school contact	51	375	373	361	12	3.2
School-based asymptomatic testing program	46	265	261	251	10	3.8
Tested because of symptoms	109	969	896	875	21	2.3
Index case symptoms
No	74	526	520	501	19	3.7	.14
Yes	141	1147	1074	1049	25	2.3	.14
Index case vaccination status
Fully vaccinated	32	347	319	318	1	0.3	.001
Partially vaccinated	6	52	51	51	0	0
Unvaccinated	176	1263	1213	1170	43	3.5
SVI overall quartile^e
<0.25 (Lowest)	67	498	498	482	16	3.2	.63
0.25-0.5 (Highest)	138	1115	1037	1009	28	2.7	.63
SVI SES quartile^e
<0.25 (Lowest)	173	1435	1360	1330	30	2.2	<.001
0.25-0.5 (Highest)	32	178	175	161	14	8.0	<.001

Abbreviations: SAR, secondary attack rate (calculated as [probable and possible transmissions / contacts tested] × 100); SES, socioeconomic status; SVI, Social Vulnerability Index; TTS, test to stay.

^{^a}

Unknown or missing values were removed if the number of unknown or missing values comprised less than 5% of the total number of contacts tested for each exposure category.

^{^b}

Grades 1 through 5.

^{^c}

Grades 6 through 8.

^{^d}

Grades 9 through 12.

^{^e}

Overall quartiles as found in the school districts included in the study.