Table II.

Epidemiological analysis of the association of the genetic island with disease

Clonal complex	Presence of the island	Patients (81)a	Carriers (212)
Invasiveb	present	36	61
	absent	2	2
Others	present	28	51
	absent	15	98
Association	island: diseasec	0.0013
	disease: “invasive” complex	0.2231
	“invasive” complex: island	0.0001

^aThe presence or absence of the element in a given isolate was determined by PCR amplification using primers, MDA-F and MDA-R, corresponding to conserved sequences near the 5′ and 3′ ends of the island.

^b”Invasive” are bacteria that belong to recognized “invasive lineages” defined on the basis of their MLST designation (ST-4, ST-11, ST-32, and ST-41/44 complexes). “Others” are bacteria that belong to phylogenetic groups other than those recognized as invasive. Because of the genetic variability of the meningococcus, some of the members of groups defined as Others are capable of causing disease.

^cStatistical associations (expressed as p-value) are the significance of the association of two variables. Hence, in the first Association row, “island: disease” is the statistical significance of the relation between possession of the genetic island and the causing of disease, taking into account the confounding effects of the (clonal) association between possession of the island and belonging to an “invasive clonal complex” and the association (by definition) between belonging to an invasive clonal complex and the causing of disease.