Acinetobacter sp can cause suppurative infections in any organ system; these bacteria are often opportunists in hospitalized patients.

Acinetobacter is ubiquitous and can survive on dry surfaces for up to a month, increasing the likelihood of patients being colonized and medical equipment being contaminated. There are many species of Acinetobacter; all can cause human disease, but A. baumannii (AB) accounts for about 80% of infections.

Diseases Caused by Acinetobacter

AB infections typically occur in critically ill, hospitalized patients. Crude death rates associated with AB infection are 19 to 54%.

The most common site for infection is the respiratory system. Acinetobacter easily colonize tracheostomy sites and can cause community-acquired bronchiolitis and tracheobronchitis in healthy children and tracheobronchitis in immunocompromised adults. Hospital-acquired Acinetobacter pneumonias are frequently multilobar and complicated. Secondary bacteremia and septic shock are associated with a poor prognosis.

Acinetobacter sp can also cause suppurative infections (eg, abscesses) in any organ system, including the lungs, urinary tract, skin, and soft tissues; bacteremia may occur. Rarely, these organisms cause meningitis (primarily after neurosurgical procedures), cellulitis, or phlebitis in patients with an indwelling venous catheter, ocular infections, native or prosthetic valve endocarditis, osteomyelitis, septic arthritis, and pancreatic and liver abscesses.

The significance of isolates from clinical specimens is difficult to determine because they often represent colonization.

Risk factors: Risk factors for infection depend on the type of infection (hospital-acquired, community-acquired, multidrug resistant—see Table 1: Neisseriaceae: Risk Factors for Acinetobacter Infection).

Table 1
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Risk Factors for Acinetobacter Infection Type of Infection Risk Factors Hospital-acquired Fecal colonization with Acinetobacter ICU stay Indwelling devices Length of hospital stay Mechanical ventilation Parenteral nutrition Previous infection Surgery Treatment with broad-spectrum antibiotics Wounds Community-acquired Alcoholism Cigarette smoking Chronic lung disease Diabetes mellitus Residence in a tropical developing country Multidrug-resistant Exposure to colonized or infected patients Invasive procedures Mechanical ventilation, particularly if prolonged Prolonged hospitalization (particularly in the ICU) Receipt of blood products Use of broad-spectrum antibiotics (eg, 3rd-generation cephalosporins, carbapenems, fluoroquinolones)

Drug resistance: Recently, multidrug resistant (MDR) AB has emerged. Spread in ICUs has been attributed to colonized health care practitioners, contaminated common equipment, and contaminated parenteral nutrition solutions.

Treatment

• Typically empiric multidrug therapy for serious infections

In patients with localized cellulitis or phlebitis associated with a foreign body (eg, IV catheter, suture), removal of the foreign body plus local care is usually sufficient. Tracheobronchitis after endotracheal intubation may resolve with pulmonary toilet alone. Patients with more extensive infections should be treated with antibiotics and with debridement if necessary.

AB has long had intrinsic resistance to many antimicrobials. MDR-AB can be resistant to ≥ 3 classes of antimicrobials; some isolates are resistant to all. Possible options include a carbapenem (eg, meropenemSome Trade Names
MERREM
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, imipenem, doripenem), a β-lactam/β-lactamase inhibitor (eg, ampicillin/sulbactamSome Trade Names
UNASYN
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), colistin, or a fluoroquinolone plus an aminoglycoside, rifampinSome Trade Names
RIFADIN
RIMACTANE
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, or both. Sulbactam (a β-lactamase inhibitor) has intrinsic bactericidal activity against many MDR-AB strains. Tigecycline, a glycylcycline antibiotic, is also effective; however, borderline activity and emergence of resistance during therapy has been reported.

Mild to moderate infections may respond to monotherapy. Traumatic wound infections can be treated with minocyclineSome Trade Names
MINOCIN
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. Serious infections are treated with combination therapy—typically, imipenem, or a β-lactam/β-lactamase inhibitor plus an aminoglycoside.

To prevent spread, health care practitioners should use contact precautions (hand washing, barrier precautions) and appropriate ventilator care and cleaning for patients colonized or infected with MDR-AB.

Last full review/revision September 2009 by Carlene A. Muto, MD, MS

Content last modified February 2012