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Additional file 1: Supplemental material.

Obstract: To characterize and analyze risky sexual networks and genetic scales to potential HIV transmission for HIV seroconcordant couples in Taizhou municipality of Zhejiang Province.HIV seroconcordant positive couples were invited as index cases to participate in an egocentric survey on HIV related risky behavior and behavioral network prior to HIV diagnosis during 2008-2011. Within-couple HIV transmission pairs were determined by the combination of both behavioral and phylogenetic analysis.Totally 27 HIV seroconcordant couples were enrolled in this study. Male spouses were more likely to report having two or more sexual partners in the past years prior to HIV diagnosis than female spouses (88.9% vs. 37.0%). Among 27 couples, 20 couples including 17 couples by male but not female spouses, 3 couples by female but not male spouses reported having two or more sexual partners (i.e., multiple sexual partners) prior to HIV diagnosis; and 7 couples by both spouses reported having multiple sexual partners. Twenty four of 27 sexual networks were determined to be HIV transmission pairs (20) or potential transmission pairs (4), 3 couples were subtyped with discordant HIV subtypes or large genetic distance and thus had different sources of HIV transmissions. In addition, among 27 concordant couples, HIV drug resistance (HIVDR) or primary HIVDR existed in 6 ART-naïve participants in 4 networks; among them, 2 networks were determined to be potential HIVDR transmission couple pairs.The HIV strains isolated in HIV infected spouses characterized with diversity and CRF01_AE was the main strain subtype. One of the spouses with risky behavior infected HIV was the main route of transmission to other spouses through unprotected sexual contacts. HIVDR was isolated from some HIV infected individuals, suggesting the risk for HIVDR transmission in married couples. The results provide enhanced evidence for urgent development of tailored prevention strategies, such as couple-based HIV counseling and testing services to reduce HIV secondary transmission.