Quantifying the impact of community quarantine on SARS transmission in Ontario: estimation of secondary case count difference and number needed to quarantine

Table 1 Numbers of index SARS cases* and non-overlapping contacts† associated with index cases.

Quarantine status	N of SARS probable and suspect index cases†	N of SARS index cases with no community contacts	N of SARS index cases with at least one community contact at any level	Group total numbers of community contacts (and secondary cases) by level of contact‡§
				All levels	Level 1	Level 2A	Level 2B	Level 3
Not in quarantine at symptom onset	267	89	178	7970 (52)	578 (37)	3186 (14)	1258 (1)	2948 (0)
In quarantine prior to symptom onset	65	39	26	528 (4)	52 (2)	164 (1)	297 (1)	15 (0)
Total	332	128	204	8498 (56)	630 (39)	3483 (15)	1555 (2)	2963 (0)

*Cases of Severe Acute Respiratory Syndrome (SARS) in the Ontario, Canada, 2003 outbreak. Includes all cases with a final disposition of suspect or probable SARS.
† Also considered, in sensitivity analyses only, were an additional 140 individuals who were potential SARS cases at some point during the outbreak and had at least one community contact, but subsequently did not meet criteria for probable or suspect SARS.
‡ Includes 8,498 community contacts with contact to one SARS case and not a second SARS case within 10 days of exposure to the first within any single 10 day period of exposure.
§ Level of contact: 1 = contact for at least 30 minutes within 1 metre; 2A = same room for ≥ 30 minutes; 2B = same room for <30 minutes or same floor, regardless of duration; level 3 = distant contact only - was in same building or large social network.

ISSN: 1471-2458