Table 3.

Comparison of indicators of recent and rapid HIV transmission between growing clusters identified at 0.5% threshold using recent diagnoses (2013–15), by minimum number of diagnoses in the past 12 months.

	Clusters with ≥ 5 diagnoses in past 12 months	Clusters with ≥ 4 diagnoses in past 12 months	Clusters with ≥ 3 diagnoses in past 12 months
Number of clusters	13	27	80
Cluster size (median, range)	16 (6–22)	12 (4─22)	5 (3─22)
Total number of people	196	330	616
No. (%) with HIV diagnosed in 2015	80 (41%)	136 (41%)	295 (48%)
No. (%) with recent infection**	52 (63%)	84 (60%)	144 (56%)
Molecular clock phylogenetic analysis
Total no. of sequences***	195	329	615
Time to most recent common ancestor for cluster (median, range)	4.7 years (1.8–7.7)	4.7 years (0.8─10.1)	3.6 years (0.4─10.1)
Total no. of nodes (transmission events)	182	302	535
Node age (median, range)	2.5 years (0.3–7.7)	2.6 years (0.3─10.1)	2.6 years (0.3─10.1)
No. (%) of nodes with age < 2 years	65 (36%)	96 (32%)	187 (35%)
Transmission rate per 100 person-years	33	31	31

Nine clusters did not achieve convergence in molecular clock analysis due to small sample size and a substantial number of diagnoses occurring in the most recent year. Sensitivity analyses excluding these clusters did not result in substantial changes to the cluster characteristics presented in the table.

^**Excludes persons for whom recency of infection could not be determined (denominator=83 for clusters with ≥5 diagnoses in past 12 months; denominator = 141 for clusters with ≥4 diagnoses in past 12 months; denominator = 259 for clusters with ≥3 diagnoses in past 12 months). Recent infection determined through the use of cross-sectional incidence assay, either BED (for 2013 diagnoses; mean duration of recent infection = 198.4 days) or Bio-Rad Avidity (for 2014 and 2015 diagnoses; mean duration of recent infection = 239.6 days).

^***Excludes persons with a missing sample collection date, which is needed for molecular clock phylogenetic analysis.`