Drug Treatment for Multidrug-resistant Acinetobacter baumannii Infections

Matteo Bassetti; Elda Righi; Silvano Esposito; Nicola Petrosillo; Laura Nicolini

Disclosures

Future Microbiol. 2008;3(6):649-660. 

In This Article

Epidemiology & Risk Factors Associated with A. baumannii Infections

The genus Acinetobacter consists of aerobic, Gram-negative bacilli that comprise 33 differentiated species, of which only ten have been named. The term 'Acinetobacter calcoaceticus-A. baumannii' complex is often used to group the most clinically relevant species.[4]

A. baumannii is ubiquitous in nature and can be recovered from soil, water and animals. In healthy humans, A. baumannii is not part of the normal skin flora, while in hospitalized patients it is frequently isolated from the respiratory tract. In general, A. baumannii colonization is limited, except during epidemic situations.[5]

A. baumannii has been associated with severe infections; possible sources have been recognized in the skin, environment and food.[6] In the hospital setting, digestive tract colonization is common, with rates as high as 41% in patients in the intensive care unit (ICU).[7]

The main characteristic of A. baumannii is the capability of surviving for prolonged periods in the environment, thus contributing to the transmission of the organism during outbreaks.[8]A. baumannii isolates are able to survive for weeks under dry conditions and have been detected on hospital bed rails until 9 days after the discharge of an infected patient, suggesting that hospital equipments could serve as a secondary reservoir for the infection.[9]

In this context, the role of environmental cleaning could be successful in controlling the spread of this organism. In a study performed in a neurosurgical ICU, high standards of cleaning have been correlated with both lower rates of environmental isolates and a lower number of patients with A. baumannii colonization and infection (p = 0.004).[10]

The capability of recognizing factors related to the presence and transmission of the organism, and the subsequent implementation of prevention measures are mandatory in limiting its spread; Villegas et al. revised the factors associated with Acinetobacter spp. outbreaks in descriptive studies between 1977 and 2000.[11] A recent case-control study identified the most significant factors in the positivity of the site of clinical culture and in a prior long exposure to multiple antimicrobials.[12] A total of 75% of the reports described predominantly ICU-related outbreaks, thus indicating that particular attention should be paid to those units. However, in the ICU setting, many organisms isolated from respiratory secretion and urine specimens could be responsible for colonization rather than infection. Among the multiple interventions undertaken (use of sterile gloves for patient contact, strict hand washing, use of disposable ventilatory equipment and so on), the identification and elimination of the source of Acinetobacter infection was noted as a major component to infection control. Additionally, a study reported a colonization rate of 20% in ICU workers' hands owing to the Acinetobacter outbreak strain. The revision of infection-control policies, with increased emphasis on routine hand hygiene between patients, cohorting of colonized patients and separation of clean and dirty areas, were also credited with halting the outbreak.[13]

Among other items involved in environmental contamination, an outbreak of bloodstream infections affecting 75 patients was reported in multiple ICUs of the same hospital owing to the improper sterilization of arterial line-pressure transducers, and an outbreak lasting over 2 years was reported in a burn unit owing to contaminated foam mattresses.[14,15] Other documented sources of infection included vials of medication, suctioning equipment, washbasin, tables, sinks and resuscitation equipment (Table 1).

Of concern, most of the current reported A. baumannii outbreaks are due to MDR isolates, with limited therapeutic options available.[16,17,18,19,20]

The genus Acinetobacter consists of aerobic, Gram-negative bacilli that comprise 33 differentiated species, of which only ten have been named. The term 'Acinetobacter calcoaceticus-A. baumannii' complex is often used to group the most clinically relevant species.[4]

A. baumannii is ubiquitous in nature and can be recovered from soil, water and animals. In healthy humans, A. baumannii is not part of the normal skin flora, while in hospitalized patients it is frequently isolated from the respiratory tract. In general, A. baumannii colonization is limited, except during epidemic situations.[5]

A. baumannii has been associated with severe infections; possible sources have been recognized in the skin, environment and food.[6] In the hospital setting, digestive tract colonization is common, with rates as high as 41% in patients in the intensive care unit (ICU).[7]

The main characteristic of A. baumannii is the capability of surviving for prolonged periods in the environment, thus contributing to the transmission of the organism during outbreaks.[8]A. baumannii isolates are able to survive for weeks under dry conditions and have been detected on hospital bed rails until 9 days after the discharge of an infected patient, suggesting that hospital equipments could serve as a secondary reservoir for the infection.[9]

In this context, the role of environmental cleaning could be successful in controlling the spread of this organism. In a study performed in a neurosurgical ICU, high standards of cleaning have been correlated with both lower rates of environmental isolates and a lower number of patients with A. baumannii colonization and infection (p = 0.004).[10]

The capability of recognizing factors related to the presence and transmission of the organism, and the subsequent implementation of prevention measures are mandatory in limiting its spread; Villegas et al. revised the factors associated with Acinetobacter spp. outbreaks in descriptive studies between 1977 and 2000.[11] A recent case-control study identified the most significant factors in the positivity of the site of clinical culture and in a prior long exposure to multiple antimicrobials.[12] A total of 75% of the reports described predominantly ICU-related outbreaks, thus indicating that particular attention should be paid to those units. However, in the ICU setting, many organisms isolated from respiratory secretion and urine specimens could be responsible for colonization rather than infection. Among the multiple interventions undertaken (use of sterile gloves for patient contact, strict hand washing, use of disposable ventilatory equipment and so on), the identification and elimination of the source of Acinetobacter infection was noted as a major component to infection control. Additionally, a study reported a colonization rate of 20% in ICU workers' hands owing to the Acinetobacter outbreak strain. The revision of infection-control policies, with increased emphasis on routine hand hygiene between patients, cohorting of colonized patients and separation of clean and dirty areas, were also credited with halting the outbreak.[13]

Among other items involved in environmental contamination, an outbreak of bloodstream infections affecting 75 patients was reported in multiple ICUs of the same hospital owing to the improper sterilization of arterial line-pressure transducers, and an outbreak lasting over 2 years was reported in a burn unit owing to contaminated foam mattresses.[14,15] Other documented sources of infection included vials of medication, suctioning equipment, washbasin, tables, sinks and resuscitation equipment ( Table 1 ).

Of concern, most of the current reported A. baumannii outbreaks are due to MDR isolates, with limited therapeutic options available.[16,17,18,19,20]

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