There is a high incidence of infection among drug users, particularly among people who inject drugs. Increased risk of infection is likely associated with poor hygiene and colonization with potentially pathogenic organisms, contamination of drugs and equipment, increased sexual risk behaviors, and impaired immune defenses. The use of parenterally administered recreational drugs has increased enormously in recent years, fueled in part by an epidemic of prescription opioid misuse and abuse. More than 2 million persons in North America are estimated to have used injection drugs in the past year.
Skin infections are associated with poor hygiene and use of nonsterile technique when injecting drugs. S aureus (including community-acquired methicillin-resistant strains) and oral flora (streptococci, Eikenella, Fusobacterium, Peptostreptococcus) are the most common organisms, with enteric gram-negatives generally more likely seen in those who inject into the groin. Cellulitis and subcutaneous abscesses occur most commonly, particularly in association with subcutaneous (“skin-popping”) or intramuscular injections and the use of cocaine and heroin mixtures (probably due to ischemia). Myositis, clostridial myonecrosis, and necrotizing fasciitis occur infrequently but are life-threatening. Wound botulism in association with black tar heroin occurs sporadically but often in clusters.
Aspiration pneumonia and its complications (lung abscess, empyema, brain abscess) result from altered consciousness associated with drug use. Mixed aerobic and anaerobic mouth flora are usually involved.
Tuberculosis also occurs in persons who use drugs, and infection with HIV has fostered the spread of tuberculosis in this population. Morbidity and mortality rates are increased in HIV-infected individuals with tuberculosis. Classic radiographic findings are often absent; tuberculosis is suspected in any patient with infiltrates who does not respond to antibiotics.
Hepatitis is very common among persons who inject drugs and is transmissible both by the parenteral (hepatitis B, C, and D) and by the fecal-oral route (hepatitis A). Multiple episodes of hepatitis with different agents can occur.
Pulmonary septic emboli may originate from venous thrombi or right-sided endocarditis.
STDs are not directly related to drug use, but the practice of exchanging sex for drugs has resulted in an increased frequency of STDs. Syphilis, gonorrhea, and chancroid are the most common.
HIV/AIDS has a high incidence among persons who inject drugs and their sexual contacts and among the offspring of infected women (see Chapter 31-05).
Infective endocarditis in persons who inject drugs is most commonly caused by S aureus, Candida (usually C albicans or C parapsilosis), Enterococcus faecalis, other streptococci, and gram-negative bacteria (especially Pseudomonas and Serratia marcescens). See Chapters 33-04, 33-26, 33-02, 33-01, and 33-16.