TABLE. Characteristics of transitional kindergarten through grade 12 public schools, by school Test to Stay status — Los Angeles County, California, September 20–October 31, 2021.

Characteristic	Did not implement TTS	Implemented TTS
Schools	(n = 1,635)	(n = 432)
No. of enrolled students*	967,188†	324,879
Student COVID-19 cases, total	4,322	812
Elementary school, no. (% of total)	2,403 (56)	341 (42)
Middle school, no. (% of total)	956 (22)	159 (20)
High school, no. (% of total)	963 (22)	312 (38)
Student close contacts of COVID-19 cases,§ total	18,729	7,511
Elementary school, no. (% of total)	9,177 (49)	2,253 (30)
Middle school, no. (% of total)	4,870 (26)	1,878 (25)
High school, no. (% of total)	4,682 (25)	3,380 (45)
Student secondary infection risk¶	1.3	0.7
Percentage of schools in the most disadvantaged neighborhoods**	74	26

Abbreviations: HPI = Healthy Places Index; LAC = Los Angeles County; TTS = Test to Stay.

* District student enrollment reported by the California Department of Education as of the 2020–21 school year.

^† LAC’s largest school district, which accounts for one third of public-school students, did not adopt TTS.

^§ Student contacts with unknown school level and age were excluded.

^¶ Secondary infection risk was defined as the number of quarantined contacts who received a positive SARS-CoV-2 test result 1–14 days after exposure divided by the total number of quarantined contacts. Limited to student school contacts.

** Based on the California HPI, which classifies California zip codes into quartiles based on a composite score of disadvantages. Indicators that determine the HPI score include economic, education, transportation, social, neighborhood, housing, clean environment, and healthcare access. Zip codes falling within the lowest HPI quartile in LAC represent the most disadvantaged neighborhoods. HPI data were missing for 16 non-TTS schools and 22 TTS schools.