Table 1. Viral Positivity Rates During Preexposure and Postexposure Periods, Comparison of 2015-2019 vs 2020 Virus Years^a.

Organism	Virus year	Preexposure (August 1-March 24)				Postexposure (March 25-July 31)
		No. of positive results	No. of tests	No. of positive results/100 tests	No. of positive results/100 d	No. of positive results	No. of tests	No. of positive results/100 tests	No. of positive results/100 d
Influenza	2015-2019	3598.4	25 197.0	14.28	304.69	695.6	8616.0	8.07	95.29
	2020	1762.5	9170.0	19.22	743.67	68.5	1608.0	4.26	46.92
Rhinovirus/enterovirus	2015-2019	3005.0	13 206.7	22.75	254.45	1303.0	5554.3	23.46	178.49
	2020	600.5	3262.6	18.41	253.38	51.5	1095.4	4.70	35.27
RSV	2017-2019	947.7	9076.5	10.44	80.25	114.3	3962.5	2.88	15.66
	2020	363.3	3998.4	9.09	153.29	27.7	1188.6	2.33	18.97
Parainfluenzavirus	2015-2019	559.4	13 288.0	4.21	47.37	281.6	5578.0	5.05	38.58
	2020	109.3	3262.6	3.35	46.12	3.7	1095.4	0.34	2.53
Coronavirus	2017-2019	367.7	8506.2	4.32	31.13	70.3	3822.8	1.84	9.63
	2020	116.7	3262.6	3.58	49.24	7.3	1095.4	0.67	5.00
Adenovirus	2015-2019	199.4	13 283.0	1.50	16.88	153.6	5578.0	2.75	21.04
	2020	58.8	3262.6	1.80	24.81	9.2	1095.4	0.84	6.30
All organisms	2015-2019	8677.7	25 765.3	33.68	734.78	2618.3	8755.7	29.90	358.67
	2020	3011.0	9905.8	30.40	1270.46	168.0	1701.2	9.88	115.07

Abbreviation: RSV, respiratory syncytial virus.

^aVirus year begins August 1 of the previous nominal year. For example, virus year 2020 runs from August 1, 2019, through July 31, 2020. This table was based on monthly count data, with March data proportionally allocated 24:7 to the 2 seasons depicted here. The RSV and coronavirus testing data available to us begin with September 2016 (virus year 2017). For other organisms, the time series begins August 2014 (virus year 2015).