Frequency, factors and costs associated with injection site infections: Findings from a national multi-site survey of injecting drug users in England

A range of bacteria can infect injecting drug users' (IDUs) injection sites, resulting in illnesses ranging from localised skin and soft tissue infections to systemic and toxin producing infections [1, 2]. These infections can result in serious morbidity requiring inpatient intervention (e.g. intensive intravenous antibiotics, surgical debridement, amputation) and sometimes death [1, 2]. The reported prevalence of recent or current infections such as abscesses, infected ulcers and cellulitus among IDUs ranges from under one in 10 in Australia [3] to between one in five and one in three in North America and Europe [4‐6]. These infections are also the most common presenting diagnoses among IDUs attending emergency departments in North America [7, 8]. Injection site infections are associated with poor hygiene and unsafe injection practices including inadequate cleaning of the hands or the injection site, needle and syringe re-use, multiple injection attempts, use of multiple injection sites, subcutaneous injection, and drawing blood back into the syringe repeatedly [3, 5, 9, 10].

There has been increasing concern in the United Kingdom (UK) about the extent of bacterial infections among IDUs [11‐13]. Reports of severe group A streptococci infections among IDUs in the UK have increased over ten fold in recent years from less than ten per annum in the mid 1990's to 143 per annum in 2004 [11]. There have also been reports of community acquired Meticillin resistant Staphylococcus aureus infection among IDUs in recent years [14, 15], and outbreaks of tetanus and wound botulism [16, 17].

Little is known about the extent of injection site infections, or the factors associated with them, among IDUs in England. These infections are, however, likely to place a considerable, and possibly increasing burden on health services as observed elsewhere [3‐5, 18]. Using survey data, this paper explores the prevalence and factors associated with self-reported symptoms of injection site infections (abscess or open wound), which are likely to be due to bacterial infection, among IDUs in England, and exploratory cost estimates of their treatment.

Data on subject-reported symptoms of an injection site bacterial infection, from a community-recruited survey of IDUs undertaken in England was used [19]. Briefly, an unlinked anonymous community-recruited survey was undertaken between autumn 2003 and summer 2005. This involved recruiting drug users who had injected during the proceeding 28 days using established methods at seven broadly representative locations across England. Participants were recruited either directly from a range of low threshold services, including drop-in centres and needle exchanges, or using indigenous fieldworkers to recruit from the community settings[20]. Those who agreed to take part, by providing verbal consent, were taken through a detailed questionnaire on their demographic, behavioural and drug use characteristics by trained interviewers. They also provided dried blood spot samples for testing for anti-bodies to hepatitis C (anti-HCV), hepatitis B core antigen (anti-HBc), and HIV (anti-HIV), and were offered a £10 acknowledgement. The questionnaire collected information on self-reported symptoms of injecting site infections, and use of health services in response to these. The survey, part of the unlinked anonymous programme, had multi-site approval from the London Research Ethics Committee and from the relevant local committees.

This survey recruited 1,058 injectors from seven locations in England: 77% (810/1,054) were male, 18% (193/1,058) aged under 25 years (median age 30 years, range 16 to 72 years), 21% (221/1,056) had been injecting for less than five years (median number of years injecting 9, range < 1 to 41 years), and the prevalence of anti-HCV was 53% (566/1,058), anti-HBc was 32% (332/1,049), and anti-HIV was 0.8% (8/1,058). Almost all had injected an opiate in the previous four weeks (999/1,058), whilst 40% (424/1,058) had injected crack-cocaine and 13% (136/1,058) an amphetamine. The majority (86%, 904/1,056) had ever been homeless (having lived in a hostel, being of no fixed abode, or living on the streets) and over half (59%, 622/1,056) had last been homeless during the proceeding 12 months.

Of the 1,058 participants, 385 (36%) reported having had a symptom of an injection site infection (either an abscess or open wound) in the previous year.

Symptoms of injection site infections appear to be common amongst IDUs in England. These infections are associated with reuse of syringes, particular injection sites, crack injecting, having hepatitis C infection and being female; with one in seven of the IDUs reporting hospital admission annually. These infections are preventable, yet based on conservative exploratory estimates they may cost the health service in England at least £15.5–19.2 million per annum.

The high prevalence of self-reported injection site infections found in this study, as found elsewhere [4, 5], are of concern and highlight the need for interventions which facilitate good injection related hygiene and practice. Firstly, this study found that the injection sites used and the reuse of injecting equipment were associated with injection site infections. Previous studies have found similar associations [9, 10]; and also associations with inadequate washing of hands or cleaning of the injection site [5, 9, 10]; multiple injection attempts before locating a vein, and the use of multiple injection sites [9, 10]. The association with femoral ('groin') injection is of particular concern as this has become more common in recent years [26], with indications of increased hospital admissions related to femoral injection among IDUs [13].

Participants injecting crack-cocaine also reported higher levels of injection site infections, as has been observed elsewhere with the injection of cocaine [6, 8, 36], and heroin and cocaine combinations [10, 27]. There is also evidence to suggest crack-cocaine use, which is associated with risky behaviours [26, 28], has become more common in the UK [29]. As in other studies, women were more likely to report an injection site infection [6, 10, 27]. This may reflect a higher awareness of infections, and/or a greater vulnerability to injection site infections among female injectors[30]. The positive association with previously receiving a prescribed substitute drug suggests that those factors leading to people not successfully completing treatment for their drug use may also put them at elevated risk of infection, though this needs further examination.

In this study homelessness – a possible marker for injection in public places – was not associated with injection site infections in the final analyses. This may reflect the relatively broad definition used. In previous studies public or semi-public injecting environments have been related to poor injection hygiene and infections [9, 10, 31]. In the UK there is increasing concern about public injection and its impact on injecting hygiene [26, 28]. Preventive interventions should thus focus on the reuse of injecting equipment, and target those injecting into groins, legs or hand, using crack-cocaine, and female injectors; they may also need to consider the role of the injecting environment [32].

The conservative cost estimate from this study – at least £15.5–19.5 million per annum – indicates that injecting site infections could place a considerable cost burden on the health care system in England. Previous work looking at the costs of problematic drug use, both injecting and non-injecting, in England indicated considerable health care costs of around £500 million per annum [33]. Whilst £25 million of this was estimated to be due to blood borne viruses (HIV, hepatitis B and C) among IDUs, the authors did not separate the costs related to injecting users. They were also not able to separate out the costs related to injecting site infections, and these may not have been fully accounted for in their estimate.

Most of the participants reporting an injection site infection sought medical advice and one third of those with an infection reported being admitted to hospital, many via an emergency department. This is consistent with other studies which suggest that IDUs tend not to seek timely medical care for their injecting-related health problems, often resulting in emergency treatment at considerable cost [8, 18, 34, 35]. The failure to seek earlier treatment probably reflects competing priorities, such as, obtaining money, purchasing and using drugs, barriers to accessing care, and poor compliance with oral antibiotic regimes and follow-up care [8, 18, 35, 36]. Emergency room use (8% of total cost) and hospital admission (> 90% of total cost) account for much of the estimated costs. These costs could be reduced substantially, past studies have shown that earlier health care seeking and targeted prevention can reduce emergency department visits, hospital bed days, and surgical procedures by more than a third [37, 38]. Whilst further work needs to identify, develop, and evaluate suitable interventions, our findings suggest a need to focus on improving injection hygiene, the better management of the body sites used for injection, and that IDUs are possibly more likely to seek care if in contact with other services.

It is important to consider the limitations and generalisability of these findings. Self-reported symptoms of injecting site infections were used in this study; however, studies have shown good concordance between self-reported symptoms and clinical diagnosis [18]. The comparative rarity, marginalisation and illegal nature of injecting drug use impedes the recruitment of a representative sample of injectors. This study aimed to minimise sampling biases and maximise representativeness by using an established community sampling strategy [20]. However, in particular, bias might arise from high-risk individuals being more likely to be captured in the survey as a result of them making greater use of the needle exchanges, and other settings, where sampling occurred. As a consequence the cost estimates could be over estimates. The cost estimates were however calculated conservatively. Firstly, they assume that IDUs seeking care only did so once each year – yet some will have more than one such episode of care per annum and a Canadian study found that half of IDUs admitted to hospital for soft-tissue and systemic infections had multiple admissions [8]. If this was the case then the estimated costs of injection site infections in England could be more than 50% greater, or at least £23 million per annum. Four days for a long hospital stay may also be conservative, as those with a serious systemic infection could stay much longer, as has found in hospitals in the USA (3 to 13 days) [4, 34, 39]. However, the available data on length of IDU hospital stays is limited, with the only UK data being 20 years old and no clinical data were collected as part of this study. The cost estimates also excluded any periods of care in high dependency units, or other high cost services, which may be required for treatment of the more severe infections. Even so, the costing, and other findings, presented here are tentative, and a more rigorous economic evaluation is required that includes UK specific data on the average hospital stay for IDUs with infection site infections and the costs of these.

Taken together these findings suggest injection site infections are common experiences among IDUs in England, and that the resultant health care costs are likely to be substantial. However, the size of these costs needs to be more fully determined. Further research is also needed to explore issues around the validity of self-reports and the relationship between these reported symptoms of infection, the severity of the infection, and health seeking behaviour.