Table 1.

Methods use to assess spatial variability of legionellosis, classification criteria for high-risk census tracts, and corresponding number of census tracts, cases, and estimated population captured by each method

Method of spatial variability	“High-risk” classification	# of census tracts identified as “high-risk”	# of cases residing in “high-risk” census tract	Estimated population within “high-risk” census tract
Unadjusted IR	IR ≥ 2 per 100,000	744	1407	3,126,058
Standardized IR	IR ≥ 2 per 100,000	724	1376	3,151,260
1% cluster detection	Detected within a cluster	93	243	327,824
50% cluster detection	Detected within a cluster	259	412	981,983
Reliable cluster detection	RS ≥ 0.5 and a RR ≥ 2	136	397	507,694

IR incidence rate, RS reliability score, RR relative risk