Outpatient Parenteral Antimicrobial Therapy in Vulnerable Populations—People Who Inject Drugs and the Homeless

Secondary outcomes included hospital length of stay (LOS), secondary bacteremia, line-tampering, and 30-day readmissions. Secondary bacteremia was defined as bacteremia with a different pathogen from the index illness, which occurred during the initial treatment course. Readmission included readmissions related to OPAT (ie, recurrent or worsening infection, treatment-related toxicities, line-tampering, secondary bacteremia, and line-associated complications).

Data collection was performed using REDCap, a data-capturing software program linked to the electronic medical record (EMR).¹⁰ Hospitalization dates and demographics were electronically populated from the EMR. Details regarding drug use, homelessness, comorbidities, diagnosis, discharge complications, clinical cure, and lost to follow-up were manually entered.

Statistical Analysis

Statistical calculations were performed using SAS (v. 9.4). Chi-square testing and analysis of variance were conducted to assess group differences in demographics, infection types, and clinical outcomes.

Primary and secondary outcomes were further evaluated by univariable logistic regression and presented as odds ratios, with the non-PWID housed group serving as the reference. Given the large number of PWID and homeless patients lost to follow-up, sensitivity analyses were conducted using the assumption that patients with unknown clinical outcomes did not achieve cure (ie, chronic infection or death). Multivariable regression was performed on the outcomes of cure and 30-day readmission to OPAT using backward elimination to select a final model, initially including potential confounders of age, sex, and relevant comorbidities (DM and HIV). We assumed that those lost to follow-up were not cured (or readmitted). Other secondary outcomes were either rare events or those of uncertain relevance (eg, hospital LOS) to be evaluated in the multivariable analysis.

Our study did not meet the definition of research by the UW’s institutional review board. It was a quality improvement project funded by a UW Medicine Patient Safety Innovations Program Grant.

Overall, 596 patients received OPAT over 16 months. OPAT patients were categorized into groups as follows: homeless PWID (9%, n = 53), housed PWID (8%, n = 48), homeless non-PWID (8%, n = 45), and housed non-PWID (75%, n = 450).

PWID were younger than non-PWID, and the majority of patients in all groups were men (Table 1). PWID were more likely to have hepatitis C. Non-PWID appeared more likely to have diabetes and be immunosuppressed.

Patients had a total of 960 types of infection (Table 1). Bacteremia was the most common infection among PWID. Osteomyelitis was the most frequent infection in non-PWID.

Discharge location varied widely (P < .001; Table 1). The majority of patients with housing (housed PWID 60.4%, housed non-PWID 59.1%) were discharged to home, although 36.7% of housed non-PWID went to nursing facilities. Among homeless patients, 58.5% of PWID and 42.2% of non-PWID were discharged to respite; 10 patients were discharged to a shelter or street. Data specific to transition from IV to oral therapy were not recorded.

Cure rates among participants with known outcomes did not differ by group (Table 1; P = .85). In a sensitivity analysis of clinical cure, assuming those with unknown outcomes were not cured, housing status and drug use were significantly associated with cure (Table 1; P < .001, in the overall test), with rates lower among housed and homeless PWID groups (50.0% and 47.2%, respectively) compared with housed and homeless non-PWID groups (73.1% and 82.2%, respectively). In the multivariable analysis after backward elimination of noninfluential measures, only PWID and housing status were associated with cure; PWID, whether housed (OR = 0.37) or not (OR = 0.33), had lower odds of cure relative to housed non-PWID (Table 2).

Secondary outcomes, evaluated on all patients regardless of cure, differed by group (Table 1). Mean LOS appeared to be shortest for homeless PWID (15.5 days versus ≥18.0 for other groups; P < .001 for overall test). Homeless PWID patients appeared more likely to have secondary bacteremia (13.2% versus <4.2% in other groups; P < .001 for overall test), line tampering (35.9% versus <2.2% in other groups; P < .001), and 30-day readmission related to OPAT (26.4% versus <16.7% in other groups; P = .004). Compared with housed non-PWID using logistic regression, homeless PWID had a higher risk of secondary bacteremia (OR = 12.9; 95% CI 3.8-37.8; P < .001), line tampering (OR 88.4; 95% CI 24.5-318.3; P < .001), and readmission for OPAT (OR 2.4; 95% CI 1.2-4.6; P = .007). After adjusting for age, sex, and comorbidities, readmission for OPAT remained elevated in homeless PWID (OR = 2.4; 95% CI 1.2-4.6). No significant differences in secondary outcomes were found between housed non-PWID and also between housed PWID and homeless non-PWID.

Among homeless persons, discharge to respite care was not associated with improved outcomes, assuming those lost to follow-up did not achieve cure. Among non-PWID discharged to respite, the cure rate was 74% (14/19) compared with 88% (23/26) discharged elsewhere (P = .20). Among PWID, 48% (15/31) discharged to respite were cured compared with 45% (10/22) discharged elsewhere (P = .83).