Acinetobacter calcoaceticus subspecies anitratus (A. anitratus) can cause nosocomially
and community acquired pneumonia. Source identification of the organism is often difficult.
An outbreak of respiratory infection and colonization with A. anitratus affecting
93 ventilated patients in all six of a hospital's intensive care units (ICUs) over
10 months is described.
In April 1984, the infection control staff started to review positive culture results
from all patients in all ICUs. At this point, information on significant isolates
was recorded by patient, site, date, genus and species, and antimicrobial susceptibility.
During the month of August 1984, an increased number of A. anitratus isolates from
sputum began to be detected. Information was expanded to include the date of hospital
admission, ICU admission, intubation, and extubation; the dates and types of all surgical
procedures; the results and dates of all prior sputum cultures; and the use of nebulized
bronchodilator medications. Monthly numbers of cases were compared for four months
prior to the outbreak, during the outbreak, and for seven months after the outbreak.
Plasmid DNA from isolates was prepared, electrophoresed, and visualized. Isolates
were designated according to the molecular weights of visualized plasmids.
Barrier precautions and improved staff handwashing did not diminish the frequency
of new cases. When pasteurized, reusable ventilator circuits and resuscitation bags
were cultured for the possibility of low-level contamination, 18 percent were positive
for A. anitratus. Terminal ethylene oxide sterilization of these devices was associated
with prompt control of the outbreak. Plasmid DNA analysis of isolates from patients
involved in the outbreak, contaminated devices, and the hands of personnel responsible
for device disinfection revealed two predominant plasmid profiles. After outbreak
control, isolates with these profiles were found much less frequently in patient specimens.
Contaminated, reusable ventilator support equipment may be a leading cause for the
extent of A. anitratus in the sputum of intubated patients. This problem is potentially
correctable by the use of terminal etyhlene oxide sterilization of reusable ventilator
circuits and resuscitation bags.