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Acinetobacter Infections

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University;


Maria T. Vazquez-Pertejo

, MD, FCAP, Wellington Regional Medical Center

Last full review/revision Jul 2020| Content last modified Jul 2020
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Topic Resources

Acinetobacter species are gram-negative organisms that can cause suppurative infections in any organ system; these bacteria are often opportunists in hospitalized patients.

Acinetobacter are gram-negative aerobic bacilli or coccobacilli that belong to the family Moraxellaceae. They are ubiquitous and can survive on dry surfaces for up to a month and are commonly carried on the skin of health care workers, increasing the likelihood of patients being colonized and medical equipment being contaminated. There are many species of Acinetobacter; all can cause human disease, but Acinetobacter baumannii (AB) accounts for about 80% of infections (1).

General reference

  • 1. Wong D, Nielsen TB, Bonomo RA, et al: Clinical and pathophysiological overview of Acinetobacter infections: A century of challenges. Clin Microbiol Rev 30(1):409–447, 2017. doi: 10.1128/CMR.00058-16.

Diseases Caused by Acinetobacter

The most common manifestations of Acinetobacter disease are

  • Respiratory infections

AB infections typically occur in critically ill, hospitalized patients. Community-acquired infections (mostly pneumonia) are more common in tropical climates. Case fatality rates associated with AB infection are 19 to 54%.

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 species can also cause wound infections and 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; or pancreatic and liver abscesses.

The significance of Acinetobacter isolates from clinical specimens, such as respiratory secretions from intubated patients or specimens from open wounds, is difficult to determine because they often represent colonization.

Risk factors

Risk factors for Acinetobacter infection depend on the type of infection (hospital-acquired, community-acquired, multidrug resistant—see table Risk Factors for Acinetobacter infection).

Table
icon

Risk Factors for Acinetobacter Infection

Type of Infection

Risk Factors

Hospital-acquired

Fecal colonization with Acinetobacter

Indwelling devices

Intensive care unit stay

Length of hospital stay

Previous infection

Surgery

Treatment with broad-spectrum antibiotics

Wounds

Community-acquired

Chronic lung disease

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 intensive care unit)

Receipt of blood products

Use of broad-spectrum antibiotics (eg, 3rd-generation cephalosporins, carbapenems, fluoroquinolones)

Drug resistance

Recently, multidrug resistant (MDR) AB has emerged, particularly in intensive care units (ICUs) in immunosuppressed patients, patients with serious underlying disorders, and patients treated with broad-spectrum antibiotics after an invasive procedure. Spread in ICUs has been attributed to colonized health care practitioners, contaminated common equipment, and contaminated parenteral nutrition solutions. Also, the number of multidrug-resistant AB infections has increased in service members who were injured and treated in Iraq, Kuwait, and Afghanistan.

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 hygiene 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 are defined as strains that are resistant to 3 classes of antimicrobials; some isolates are resistant to all. Before susceptibility results are available, possible initial options include a carbapenem (eg, meropenem, imipenem, doripenem), colistin, or a fluoroquinolone plus an aminoglycoside, rifampin, or both. Sulbactam (a beta-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 have been reported. Minocycline has in vitro activity as does the novel siderophore-cephalosporin antibiotic, cefiderocol (1).

Mild to moderate infections may respond to monotherapy. Traumatic wound infections can be treated with minocycline.

Serious AB infections are treated with combination therapy—typically, carbapenems (imipenem or meropenem) or ampicillin/sulbactam plus an aminoglycoside; when drug resistance is extreme, tigecycline or the combination of colistin plus minocycline may be the only available options.

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.

Treatment reference

  • 1. Munier AL, Biard L, Rousseau C, et al: Incidence, risk factors, and outcome of multidrug-resistant Acinetobacter baumannii acquisition during an outbreak in a burns unit. J Hosp Infect 97(3):226–233, 2017. doi: 10.1016/j.jhin.2017.07.020.

Key Points

  • A. baumannii (AB) accounts for about 80% of Acinetobacter infections and tends to occur in critically ill, hospitalized patients.

  • The most common site for infection is the respiratory system, but Acinetobacter species can also cause suppurative infections in any organ system.

  • Multidrug-resistant AB has become a problem; use multidrug treatment chosen based on susceptibility testing.

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