Table 2.

Occurrence of SARS-CoV-2 infection in seropositive and seronegative healthcare workers

Center	SARS-CoV-2 serostatus	No. subjects (%)	No. subjects with SARS-CoV-2 RNA positive swab (% of seropositive or seronegative subjects)	Odds ratio (95% confidence interval)
Pavia	Positive	321 (8.5)	7 (2.18)	0.33 (0.15-0.69)
	Negative	3441 (91.5)	219 (6.36)
Piacenza	Positive	965 (29.1)	14 (1.45)	0.24 (0.14-0.42)
	Negative	2356 (70.9)	136 (5.77)
Lecco	Positive	174 (6.9)	5 (2.87)	0.35 (0.15-0.81)
	Negative	2353 (93.1)	185 (7.86)
Total	Positive	1460 (15.2)	26 (1.78)	0.26 (0.17-0.38)
	Negative	8150 (74.8)	540 (6.63)