This retrospective, observational study is based on data from a follow-up cohort of people engaged in OAT who inject cocaine and heroin actively in the last six months and were attending a mobile harm reduction unit located in the outskirts of Madrid between 1 January 2016 to 30 December 2019. This mobile unit is based on a low-threshold approach consisting of no entry requirements, no appointments, a non-judgmental nature, flexibility, and on-site healthcare on demand.
This study was conducted in a mobile harm reduction unit, where a comprehensive, multidisciplinary team actively cared for and followed PWID with limited access to standard healthcare. Several services were offered, including needle-exchange programs (NEP) consisting of safe disposal for used needles, distributing naloxone, OAT, frequent testing for infectious diseases, dispensing treatment for chronic diseases, harm reduction education, counseling, and social support on-demand and as low-threshold. This mobile harm reduction unit has five vans used by health workers and offers different services. Despite these provisions, due to the absence of mobile safe injection rooms, people inject alone, in pairs, or groups in the street, cars, parks, tents, accommodations, or in their houses.
In Madrid, people with opioid use disorder engaged in harm reduction services are dispensed liquid formulations of methadone hydrochloride and no other opiate substitutes are allowed in this setting in order to avoid illegal sale or misuse of opiate pills. However, when individuals are in inpatient hospital care, all individuals continue methadone treatment and doses are increased to overcome opiate cravings.
Registered clinical data at the mobile harm reduction unit were reviewed to identify cases of severe bacterial injection-related infections that required hospital admission in people on OAT (discharge summaries through standardized coding system (ICD-10)). Information related to demographic data, retention in OAT, and type of SSTI was collected from medical records, as well as local electronic data systems at the mobile harm reduction unit. The clinical information and outcomes of each event were collected from the electronic medical records at the hospital.
Healthcare personnel at the mobile harm reduction unit interviewed each participant with a short questionnaire when they started OAT and recorded their drug use and clinical data. Information regarding the type of drug use and route of use was collected and based on self-reports.
Severe injection-related infections were defined as the presence of any of the following types of IDU-related infections that required hospital admission and occurred during the follow-up: complicated SSTI, bacterial isolates from the blood (bacteremia), infective endocarditis (IE), or bacteremia with spread to other non-cardiac locations.
Complicated SSTIs were defined as cases of skin abscesses or ulcers, extended cellulitis, myositis, or fasciitis at the injecting site. An episode of IE diagnosed at the hospital was defined as definite or possible according to the modified Duke criteria (17). Bacteremia was defined as an isolation of any bacteria from the bloodstream obtained through blood culture systems in conjunction with fever and other symptoms of infection without conclusive evidence of disseminated infection to other organs. Bacteremia with spread to other non-cardiac locations was defined by an isolate of any bacteria considered clinical and microbiologic, related to IDU, with hematogenous spread to other non-cardiac organs, such as discitis, arthritis, septic emboli, osteomyelitis, or spondylitis.
Hospital readmissions that occurred within 90 days from the discharge date were considered as relapses and not a new episode of an SSTI. However, if the readmission occurred within the first 90 days from discharge and the microorganism in the blood culture was different from the previous episode, it was classified as a new event. All the readmissions for the same person after day 90 from hospital discharge were considered as new episodes of SSTIs and recorded as separate events.
Discharges from the hospital were classified as medical advice or PDD, and no data were available to describe how many days of antibiotics were missed by PDD.
For this analysis, the identification of pathogens was verified by bloodstream culture results identified from at least one sterile site culture or obtained through a surgical procedure. The events of severe injection-related infections with the isolation of Staphylococcus aureus were classified in methicillin-sensitive (MSSA) or methicillin-resistant (MRSA).
To calculate the length of stay at the hospital, we considered the admission date for any severe injection-related infections and the discharge date for planned discharges or PDD, or the death date in those cases with a fatal outcome. If readmissions due to a relapse occurred, only the first hospital admission was considered.
Categorical variables were compared using the Pearson chi-squared test or Fisher exact test. Continuous variables were compared using the Wilcoxon rank-sum test for independent variables. The Kaplan-Meier method was used to estimate the overall incidence density and incidence density of severe injection-related infections according to the type of infections. The time at risk for any severe injection-related infection was calculated from the date of initiation in OAT at the mobile harm reduction unit to the date of hospital admission for any severe injection-related infections or the date last in OAT. Participants remaining persistently free of severe injection-related infections were censored at the time of their last day in OAT prior to 30th December 2019.
Cox proportional hazard regression analysis was used to assess factors associated with time to event of severe injection-related infection. In the unadjusted analyses, potential predictors were determined according to previous reports and included: age (per year), sex, nationality, mental health illness, HIV and HCV infection. All variables with p < 0.05 in the univariate analysis were included in the multivariate regression models using an Akaike Information Criterion (AIC) method approach. Statistical significance was set at p < 0.05; p-values were two-sided.
Study data were collected and managed using REDCap (Research Electronic Data Capture) tools hosted at “Asociación ideas for Health” (18). REDCap is a web-based software platform designed to support data capture for research studies. Analyses were performed using R software (R Foundation, Vienna, Austria).