Determinants of hospitalization for a cutaneous injection-related infection among injection drug users: a cohort study

Cutaneous injection-related infections (CIRI), which include cellulitis and abscesses, are among the primary causes of hospitalization among individuals who inject drugs (IDU) [1–4]. Hospitalizations due to CIRI carry considerable economic burden [3, 5, 6]. Complications of CIRI that are more likely to require hospitalization include, but are not limited to: osteomyelitis [7], bacteremia and sepsis [8, 9], endocarditis [10, 11], septic arthritis [7, 12], ulcer [9], thrombophlebitis [13, 14] and myositis [9].

A recent report by Hope et al. (2008) suggested that healthcare associated costs for CIRI among IDU in England were substantial, ranging from £15.5 million to £30.0 million per annum [5] ($27.1 to $52.4 million Canadian dollars). In 2001, Palepu et al. reported that of the IDU seen at St. Paul's Hospital, an urban hospital in Vancouver, Canada, 35% had been hospitalized and a third of these hospitalizations were due to a CIRI or related infectious complication [1]. Hospitalization was expensive with hospital utilization cost per day reported to be $610 Canadian dollars (C$610) (95% confidence interval {CI}: C$C576- C$645) [1].

North America's first supervised injection facility (SIF) opened in Vancouver's Downtown Eastside (DTES) in 2003. Within the SIF, IDU can inject pre-obtained drugs under the supervision of nurses. Individuals visiting the SIF are provided with sterile injecting equipment and emergency intervention in the event of an overdose, as well as primary medical care and addiction treatment, either on site or through referral. While several studies have pointed to the positive impact of the SIF on public disorder [15], HIV risk behaviour [16], management of overdose [17, 18] and use of addiction treatment [19], its role with regard to hospitalization for CIRI remains unknown. However, recent research highlights that CIRI are a medical issue of concern among users of the SIF. Over a two year period, 6-10 per cent of IDU had a CIRI at time of interview [20]. In the present analysis, using longitudinal data, we examined predictors and cost of hospitalization for a CIRI or related infectious complication among IDU using the SIF.

During the study period (1 January 2004 to 31 January 2008), 1083 individuals were recruited into the SEOSI cohort and 901 (83%) reported at least one follow-up visit. The median age among SEOSI participants was 38.4 years (interquartile range {IQR}: 32.7-44.3) and 314 (29%) were female. The median follow-up duration after recruitment into the cohort was 21.4 months (IQR: 13.1-24.6). During the study period, 99 (9%) participants were admitted to St. Paul's Hospital, yielding an incidence density of hospitalization for a CIRI or related infectious complication of 6.07 per 100 person-years (95% CI: 4.96 - 7.36). Among all hospital admissions among SEOSI participants, 49% (216 of 442) were related to a CIRI or related infectious complication. A total of 216 hospitalization events occurred among 99 individuals for a CIRI or related infectious complication. Among the 99 hospitalized SEOSI participants, 47 received CIRI care at the SIF during the study period. A total of 145 SEOSI participants were referred by a nurse at the SIF while 63 participants were referred and visited the ED. In addition, 115 SEOSI participants were referred but subsequently not hospitalized. Importantly, 60% (28/47) of those who received CIRI care at the SIF were referred to the hospital by a nurse at the SIF and subsequently sought treatment at the hospital. Individuals with an ED visit who were referred by a nurse were more likely to be hospitalized within three days (p = 0.011). Further, those who were referred to the hospital by a nurse at the SIF were significantly more likely to have been seen by a nurse at the SIF for a CIRI (8 nurse visits for a CIRI [IQR: 3-16]) compared to those that were not referred to a hospital (1 nurse visit for a CIRI [IQR: 0-4]) (p < 0.001). Virtually all patients are admitted to the hospital from the Emergency Department (ED).

In the present study, being referred by a nurse at a SIF was independently associated with an elevated rate of hospitalization. Importantly, participants who had been referred to the hospital by a nurse at the SIF had a significantly shorter length of stay in hospital despite adjustment for HIV infection and other potential confounders. This finding indicates that nurses facilitate hospital utilization as well as providing early intervention that prevents lengthy and expensive hospital visits for a CIRI or related infectious complication. According to the cost savings calculation based on the length of stay reduction, SIF nurse referral resulted in a minimum saving of C$2,136 per admission. However, it is important to note that variability in treatment costs exists in the CIRI and related infectious complications included in this investigation.

Using the same cohort, the risk factors for the outcome of developing a CIRI have been reported to include being female, living in unstable housing, borrowing syringes, requiring help injecting and injecting cocaine daily [20]. Some factors differ from risk factors in other cities. For example, research from San Francisco reports an associated between developing a CIRI and frequent black tar heroin injection [2] whereas in Vancouver, frequent cocaine injection has been associated with developing a CIRI [20]. The present study evaluated the predictors of the outcome of hospitalization for a CIRI or related infectious complication. The predictors of hospitalization for a CIRI or related infectious complication included being HIV positive and referred to the hospital by a nurse at the SIF. Future research investigating outcomes, including mortality from a CIRI or related infectious complication among those referred compared to those not referred to the hospital by a nurse at the supervised injection facility would support our understanding of the potential impact of nurse referral. Interestingly, being HIV positive was not a risk factor for the development of CIRI but was a predictor of hospitalization for a CIRI or related infectious complication.

As noted above, an increased risk of hospitalization for a CIRI or related infectious complication was observed among HIV positive participants. This finding is consistent with previous research on hospitalization among IDU in this setting [1]. Individuals with HIV may be more likely to be treated as an inpatient as opposed to an outpatient (i.e., HIV positive patients with abscesses may be more likely to get admitted to the hospital than HIV negative patients with abscesses). A potentially elevated susceptibility to bacterial infections [8, 24] as well as known high-risk drug injection practices in this subpopulation [25, 26] may related to why HIV positive participants in this study had elevated rates of hospitalization. Further elucidation of this finding with a larger sample of HIV positive IDU is necessary to examine this important research question.

After controlling for factors that are known to be associated with hospitalization [1, 27], referral from an SIF nurse remained a strong predictor of hospitalization. Findings from this study confirm existing qualitative research indicating that nurses at the SIF provide CIRI-related care and play a key role in enhancing access to medical care among participants who have infections or injuries of greater severity [28]. Hospital care for more severe forms of CIRI is essential since local hospitals provide treatment to CIRI not available at the SIF (e.g., incision and drainage of an abscess, intravenous antibiotic therapy as well as diagnostic tools and therapy appropriate for complications). Further, given that the average length of stay in hospital for those referred to the hospital by a nurse at the SIF was significantly shorter, it may be that nurses at the SIF are helping reduce the incidence of late presentation of complications, such as osteomyelitis, that are often lengthy and are particularly costly to the healthcare system [7]. Although our study design does not allow us to infer causation, it is noteworthy that this association persisted in multivariate analyses. This may reflect prompt referral as well as the preventative effect of the SIF on serious infections [16].

There are several examples of efficient and cost effective community-based treatment services that may inform changes in the provision of care that is required in order to reduce the incidence of hospitalization of a CIRI or related infectious complication in our setting. In its first year of operation, the Integrated Soft Tissue Infection Services (ISIS) Clinic in San Francisco, California, resulted in a 47% decrease in surgical service admissions and an estimated savings of over $8.0 (C$8.4) million for costs related to CIRI [29]. In addition, a wound management clinic operated in conjunction with a syringe exchange program in Oakland, California [30]. It was found that the average cost per individual treated at this wound management clinic was $5.0 (C$5.2), substantially lower than equivalent hospital costs of $185.0 (C$193.4) and $360.0 (C$376.3) [30]. Given the success other cities have had in implementing additional medical treatment for CIRI in the community, we recommend initiating provision of on-site incision and drainage for abscesses and administration of antibiotic therapy at the SIF or in a nearby community setting. Further, to prevent development of CIRI, it may be of value to screen and treat for MRSA at the SIF or at the SEOSI research site. In our setting, expanding the capacity to provide primary care in an integrated manner is warranted.

There are limitations of the present study to consider when interpreting this data. Firstly, St. Paul's Hospital was the only facility linkage that was conducted. However, this is the primary hospital serving the SIF catchment area and is accessed extensively by the IDU population in the DTES [1, 27, 31]. Secondly, our study relies on self report to obtain drug use and other behavioural variables. However, self report among IDU is considered valid [32] and hospital utilization and nurse referral were accessed directly from databases within the hospital and at the SIF, respectively. Thirdly, a limitation of this analysis is that a low sample size of HIV positive participants precluded our ability to conduct further analyses on this association. Additional research is required with a larger sample of HIV positive individuals to better elucidate this finding. Fourthly, additional research is required to better understand why a shorter length of stay is seen among SEOSI participants referred by a nurse at the SIF to the hospital. It is possible that nurses may be referring to the hospital SEOSI participants that require shorter lengths of stay (e.g., abscess versus osteomyelitis). However, in our study, individuals with an ED visit who were referred by a nurse were significantly more likely to be hospitalized within three days. Similarly, Binswanger et al. found ED use for CIRI to be associated with hospitalization and also death [33].

In summary, we found high levels of hospitalization for a CIRI or related infectious complication among local IDU. Being HIV positive and being referred to the hospital by a nurse at the SIF, as opposed to self referral to the hospital, were both independently and positively associated with an increased likelihood of hospitalization. Participants who had been referred to the hospital by a nurse at the SIF had a significantly shorter length of stay in hospital as compared to those who were not. These findings indicate that nurses at the SIF play a critical role in terms of referring individuals who require hospitalization for a CIRI or related infectious complication to the hospital, which may result in shorter and less expensive hospital visits. Expanded management of CIRI in the community may reduce the need for referral to the hospital, further reducing the cost of caring for this common clinical problem among IDU.