IDU has been prevalent in the US since the early 1900s. Intravenous injection is the most common means of administration but users may also inject drugs using subcutaneous (ie, skin popping) or intramuscular techniques. These practices can foster various infectious and other medical complications, especially HIV, hepatitis B virus (HBV), hepatitis C virus (HCV), and bacteremia/endocarditis (Table 1). The sharing of needles and syringes is the major risk factor for the acquisition of blood-borne pathogens such as HIV, HBV, and HCV, whereas the use of contaminated drugs and nonsterile drug paraphernalia and injection techniques increases the possibility for systemic infections, such as bacteremia, endocarditis, and cellulitis.1–3
Infections Associated with Injection Drug Use
HIV. The Centers for Disease Control and Prevention (CDC) estimates that there are approximately 1.2 million people living with HIV, with approximately 50,000 new infections occurring annually in the US—a number that is, fortunately, trending downwards.4 Nonetheless, it is estimated that of the new annual infections, approximately 11% are due, in part, to IDU (7% directly attributable to IDU and 4% related to high-risk sexual behaviors combined with IDU).4,5 Extrapolating yearly data on IDU, approximately 10% to 40% of people who inject drugs (PWIDs) are infected with HIV; therefore, an estimated 260,000 people with HIV potentially acquired the virus through IDU.6 The IDU transmission rate of HIV has been estimated to be 1 in 150 exposures.7 As many as one-third of the PWIDs share needles and syringes, which dramatically increases the risk of HIV infection.8
People who have HIV and inject drugs often lack access to appropriate health care in general as well as HIV treatment. The CDC estimates that ≥60% of people with HIV who also inject drugs are either homeless or have been incarcerated; ≥40% also lack health insurance, making it difficult to find appropriate care, start HIV therapy, or start substance-dependence treatment.8 Treatment access is particularly important given that a major advance in HIV care has been the advent of combination antiretroviral therapy, which has substantially extended life expectancy and is currently recommended no matter the CD4 T-cell count or HIV viral load (Table 2).
Current Recommendations for Antiviral Treatments for HBV, HCV, and HIV
HBV. According to the CDC, approximately 20,000 new HBV cases occur each year in the US, with 17% of those cases resulting from IDU; approximately 4% to 6% of PWIDs are infected with HBV.9,10 Prevention of virus acquisition can be accomplished through vaccination, with ≥90% efficacy. Currently, the CDC and Advisory Committee on Immunization Practices recommend HBV vaccination for all adults who use injection drugs and are seronegative for HBV infection. A person who presents after an exposure can be given the HBV vaccine series or the HBV vaccine series with HBV immunoglobulin if the contact source is HBV positive.11 Like the patients with HIV as described above, people with HBV often lack access to medical care, making them less likely to receive appropriate screening and treatment (Table 2).
HCV. There are approximately 30,000 new cases of HCV annually, with that number rising recently.9 The age distribution of HCV is bimodal, with most patients with HCV having been born between 1945 and 1965 in which the likely transmission was through blood transfusions and IDU earlier in life, whereas young adolescents/adults acquire the virus mainly from IDU (although high-risk sexual practices are also known to be a factor).12 IDU accounts for a large proportion of new infections, with estimates ≥54% in the US, and at 90% globally.13 Due to the indolent state and often asymptomatic nature of the virus, 40% to 80% of all PWIDs currently have HCV,14,15 which is higher than the prevalence of HIV because HCV is more transmissible.
Because there is no vaccine for HCV, prevention efforts currently focus on needle-exchange programs and education about proper injection techniques as well as the identification of those people infected with HCV. The CDC recommends screening for HCV infection by using a serum HCV antibody test. People who continue to use intravenous drugs should be screened periodically, although no recommended time interval for screening exists.16
It is important to realize that, although acute infection may be asymptomatic or manifest with only mild symptoms, if left untreated, those people will ultimately develop cirrhosis and/or hepatocellular carcinoma. Moreover, concurrent heavy alcohol use is associated with worse outcome.17 Thus, prompt identification of people with HCV is vital and should lead to assessment of the degree of liver damage, determination of treatment needs, and education to help regulate behaviors related to substance abuse. In this light, over the past 3 years there has been a revolution in the available HCV treatments. These new agents are direct antivirals targeted against HCV and have >90% cure rates.18 Recommendations for HCV treatment are constantly changing19 (Table 2). Further details related to HCV treatment with concurrent psychiatric diseases is reviewed elsewhere;20 exact treatment plans should be discussed with a hepatologist.
Bacteremia/endocarditis. IDU can lead to the transmission of other nonviral, blood-borne illnesses. Most nonviral infections among PWIDs stem from improper cleaning of skin and needles prior to injection, which can result in skin flora (eg, bacteria or fungi) being injected. Thus, active drug users may have various physical examination results indicative of IDU. Common injection sites include the veins of the forearm, wrist, antecubital fossa, ankle, and dorsum of one's hand; therefore, patients who inject frequently may exhibit track marks, scarring, and toxin build-up along the length of the veins. “Skin popping,” injecting drugs subcutaneously or intradermally rather than intravenously, can often produce nodules or open wounds seen on physical examination. Local cellulitis or skin abscesses can occur from these two methods of drug injection as well; although these are generally self-treated, they may be evident in one-third of PWIDs and sometimes can progress to more severe infections such as necrotizing fasciitis.21
Of greater concern is development of bacteremia from commensal skin flora such as Staphylococcus aureus (including methicillin-resistant strains or MRSA) or Streptococcus species, which can lead to widespread dissemination and result in complications including brain abscess, osteomyelitis, renal abscess, or even endophthalmitis. Of these complications, endocarditis, an infection of the cardiac valves or other endovascular structures, may be particularly common. Actual incidence rates of bacterial endocarditis in PWIDs are unclear, but estimates vary from 0.15% to 2% per year.22 Approximately 76% of bacterial endocarditis in PWIDs occurs on the right side (usually the tricuspid valve), which causes more morbidity, albeit less mortality with left-sided endocarditis.22 The mortality rate for right-sided endocarditis is approximately 6%, with vegetation size (larger worse than smaller) and etiology (fungal worse than bacterial) being the major determinants of death.23
A major issue with managing patients with infective endocarditis is ensuring adequate treatment. The mainstay of therapy is a prolonged course of intravenous antibacterial drugs, but many of the patients are unwilling to remain hospitalized for the full duration of treatment.