The risk of HIV or hepatitis C in people who inject drugs is influenced as much by their social interactions and the places they inject as by other risk factors, according to a study published today in eLife.
The findings could help direct public health efforts to the places where HIV and hepatitis are most often transmitted, allowing more effective use of harm reduction services and more quickly interrupting transmission of the disease.
India has one of the highest HIV and hepatitis C burdens resulting from injection drug use. Efforts to stop the spread of these diseases are hampered by a suboptimal understanding of the role that social networks can play in the spread of infectious diseases, especially in a population that includes many homeless and hard-to-reach people.
Social interactions can be used to interrupt disease transmission and can be useful in controlling epidemics among populations linked by a common behavior – in this case, injecting drugs – according to the authors. However, the development of network-based interventions in this population is difficult because the structure of the network is often unknown or poorly understood, especially indirect networks (as in “friend of a friend” connections).
To address this problem, the authors sought to understand the structure of social ties (injection partners) and spatial ties (places where people inject) of those who inject drugs in New Delhi, India. They started by recruiting an initial group of 10 people who inject drugs, who then provided the names of the injection partners. They were asked to recruit these contacts into the study. These recruits were, in turn, invited to do the same. The study was set up so that none of the contacts were duplicated, but if a person was referred by more than one contact, then they were interconnected with each of the named contacts. The result was a network of direct and indirect connections between 2,512 people who inject drugs, mostly men and aged 26 on average, covering a total of 181 sites within a 20 km radius.
The team then offered participants tests for HIV and hepatitis C, with appropriate referrals to care where appropriate, and asked them to complete surveys to provide additional information on factors such as level of education, homelessness, frequency of injections, type of drug injected, sexual relations. activity and needle sharing.
At the start of the study, 37% were HIV positive and 65% had antibodies to hepatitis C, with 80% of these people having an active infection. Most did not know they had hepatitis C. Of people living with HIV, 65% were directly related to someone else who was HIV positive. Of those with active hepatitis C infection, 74% were directly related to at least one other person with active infection.
The most important determinant of testing positive for HIV or hepatitis C was injection instead of the most popular injection – this increased the risk of infection by 50%. Even if a person did not personally inject at this site, their risk of infection increased if one of their injection partners did. For every person separating a given individual from the most popular location, the likelihood of having HIV or hepatitis C has decreased by 14%. Likewise, for every person separating a given person from a person who tested positive for HIV or hepatitis C, the likelihood of having both HIV and hepatitis C decreased by 13%.
The results show that infection with HIV and hepatitis C is not only associated with individual risk factors such as age, education or frequency of injection, but also with direct links and indirect with social and spatial networks, even after taking into account individual characteristics. The study provided a better understanding of the network structure of people who inject drugs in New Delhi and highlighted the role of indirect connections and space on the burden of disease. The authors say it also urges rethinking “networks” to incorporate indirect network connections and spaces when thinking about interventions to interrupt disease transmission.