Injection Drug Use–Related Infections

Essentials of Diagnosis

• Common infections that occur with greater frequency in persons who inject drugs

  • Skin infections

  • Hepatitis A, B, C, D

  • Aspiration pneumonia

  • Tuberculosis

  • Pulmonary septic emboli

  • Sexually transmitted diseases

  • HIV/AIDS

  • Infective endocarditis

  • Osteomyelitis

  • Septic arthritis

General Considerations

SKIN INFECTIONS

• Associated with poor hygiene and use of nonsterile injection technique

• Most common organisms

  • Staphylococcus aureus (including methicillin-resistant strains)

  • Oral flora (streptococci, Eikenella, Fusobacterium, Peptostreptococcus)

• Enteric gram-negative organisms are less common except in those who inject into the groin

HEPATITIS

• Very common among persons who inject drugs habitually

• Transmissible both by the parenteral route (hepatitis B, C, and D) and by the fecal–oral route (hepatitis A)

• Multiple episodes of hepatitis from different agents can occur

ASPIRATION PNEUMONIA

• Results from altered consciousness associated with drug use

• Mixed aerobic and anaerobic mouth flora are usually involved

TUBERCULOSIS

• Infection with HIV has fostered the spread of tuberculosis

PULMONARY SEPTIC EMBOLI

• From venous thrombi or right-sided endocarditis

SEXUALLY TRANSMITTED DISEASES

• Related to the practice of exchanging sex for drugs or money for drugs

• Syphilis, gonorrhea, and chancroid are the most common

HIV/AIDS

• High incidence among persons who inject drugs, among their sexual contacts, and among the offspring of infected women

INFECTIVE ENDOCARDITIS

• Most common organisms

  • S aureus

  • Candida (usually C albicans or C parapsilosis)

  • Enterococcus faecalis

  • Other streptococci

  • Gram-negative bacteria (especially Pseudomonas and Serratia marcescens)

• Right-sided heart involvement

  • Common

  • Infection of more than one valve is not infrequent

OTHER VASCULAR INFECTIONS

• Septic thrombophlebitis

• Mycotic aneurysms result from direct trauma to a vessel with secondary infection

• Aneurysms result from hematogenous spread of organisms

OSTEOMYELITIS AND SEPTIC ARTHRITIS

• Osteomyelitis usually results from hematogenous distribution of injected organisms or septic venous thrombi

• While staphylococci—often methicillin-resistant—are common organisms, also found are Serratia, Pseudomonas, Candida (often not C albicans), and other pathogens rarely encountered in spontaneous bone or joint disease

Demographics

• More than 2 million persons in North America are estimated to have used injection drugs in the past year

Symptoms and Signs

SKIN INFECTIONS

• 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

RIGHT-SIDED INFECTIVE ENDOCARDITIS

• Septic pulmonary emboli support this diagnosis, especially in the absence of murmurs

OTHER VASCULAR INFECTIONS

• Mycotic aneurysms occur

  • Most commonly in femoral arteries

  • Less commonly in arteries of the neck

• Aneurysms

  • Frequently involve intracerebral vessels and are seen in association with endocarditis

OSTEOMYELITIS

• Involves the

  • Vertebral bodies

  • Sternoclavicular joints

  • Pubic symphysis

  • Sacroiliac joints

  • Other sites

Differential Diagnosis

• Community-acquired pneumonia

• Endocarditis

• Complications of endocarditis, eg, pulmonary septic emboli, epidural abscess, osteomyelitis

• Skin abscess, cellulitis, myositis, necrotizing fasciitis

• Pelvic inflammatory disease

• Urinary tract infection

Laboratory Tests

• Appropriate cultures (blood, urine, and sputum)

• Complete blood count, liver chemistries, urinalysis

Imaging Studies

• Chest radiograph

• Classic radiographic findings are often absent in HIV patients with tuberculosis; any patient with infiltrates who does not respond to antibiotics is suspect

• Pain and fever precede radiographic changes of osteomyelitis and septic arthritis, sometimes by several weeks

Diagnostic Procedures

• Transesophageal echocardiogram

  • May be helpful if blood cultures are positive for an organism that is an unusual cause of endocarditis

  • Can detect vegetations with 90% sensitivity

  • Normal study is strong evidence against endocarditis

• In a febrile individual who injects drugs, after obtaining appropriate cultures (blood, urine, and sputum if the chest radiograph is abnormal), empiric therapy is begun (Table 30–5)

• If the chest radiograph suggests a community-acquired pneumonia (consolidation)

  • Outpatient therapy with a third-generation cephalosporin is begun

  • Ceftriaxone, 1 g intravenously every 24 hours; plus azithromycin, 500 mg orally or intravenously every 24 hours, or doxycycline, 100 mg orally or intravenously twice daily

• If the chest radiograph suggests septic emboli (nodular infiltrates)

  • Therapy for presumed endocarditis is initiated

  • Usually vancomycin 15 mg/kg/dose every 12 hours intravenously (due to the high prevalence of methicillin-resistant S aureus and the possibility of enterococcus)

• If the chest radiograph is normal and no focal site of infection can be found

  • Endocarditis is presumed

  • While awaiting the results of blood cultures, empiric treatment with vancomycin is started

• If blood cultures are positive for organisms that frequently cause endocarditis in injection drug users, then endocarditis is presumed to be present and treated accordingly

• If blood cultures are positive for an organism that is an unusual cause of endocarditis, patient should be evaluated for an occult source of infection

• If blood cultures are negative and the patient responds to parenteral antibiotics

  • Therapy should be continued for 7–14 days

  • Oral therapy can be given once an initial response has occurred

• In every patient, careful examination should be done for an occult source of infection (eg, genitourinary, dental, sinus, gallbladder)

• Clinicians also can have a significant role to play in integrating treatment of opioid use disorder (OUD) when patients present with infectious disease complications, including by

  • Screening for OUD

  • Undergoing specific training for and prescribing OUD medications (such as buprenorphine)

  • Treating withdrawal symptoms

  • Linking patients to community-based treatment on hospital discharge

Complications

• Aspiration pneumonia

  • Complications include lung abscess, empyema, and brain abscess

Prevention

• Immunizations against hepatitis A and B

• Clean needle use will decrease transmission of blood-borne pathogens

When to Refer

• Patients with OUD to treatment programs

• Any patient with suspected or proven infective endocarditis

• Patients with persistent bacteremia

When to Admit

• Persons who inject drugs and have fever

• Patients with abscesses or progressive skin and soft tissue infection that require debridement