Chest
Volume 115, Issue 1, January 1999, Pages 178-183
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Clinical Investigations in Critical Care
The Role of Anaerobes in Patients With Ventilator-associated Pneumonia and Aspiration Pneumonia: A Prospective Study

https://doi.org/10.1378/chest.115.1.178Get rights and content

Context

Aspiration of oropharyngeal material, with its high concentration of anaerobic bacteria, has been implicated in the pathogenesis of both ventilator-associated pneumonia (VAP) and aspiration pneumonitis (AP). Consequently, patients with these disorders are usually treated with antimicrobial agents with anaerobic activity.

Objective

To determine the incidence of anaerobic bacteria in patients with VAP and AP.

Design

Prospective, nonrandomized, interventional study.

Setting

University-affiliated community teaching hospital.

Patients and interventions

We performed sequential blind protected specimen brush (PSB) sampling and mini-BAL in 143 patients with 185 episodes of suspected VAP and 25 patients with AP who required mechanical ventilation. Quantitative aerobic and anaerobic cultures were performed on all specimens. Pneumonia was considered to be present when either > 500 cfu/mL cultured from blind PSB sampling or > 5,000 cfu/mL cultured from mini-BAL were present.

Results

Using the predefined criteria, bacterial pneumonia was diagnosed in 63 of 185 suspected VAP episodes (34%) and 12 of 25 patients with AP (48%). At least one dose of an antibiotic was given in the 24 h prior to bacteriologic sampling in 106 suspected VAP episodes (57%) and in 12 patients with AP (48%). More than one pathogen was isolated from 11 VAP and four AP patients. Pseudomonas aeruginosa, Staphylococcus aureus, and enteric Gram-negative organisms were isolated most frequently from patients with VAP. In the patients with AP, enteric Gram-negative organisms were isolated in patients with GI disorders and Streptococcus pneumoniaeand Haemophilus influenzae predominated in patients with“ community-acquired” aspiration. Only one anaerobic organism was isolated from the entire group of patients; Veillonella paravula was isolated from a blind PSB specimen in a patient with suspected aspiration pneumonia.

Conclusion

Despite painstaking effort, we were able to isolate only one anaerobic organism (nonpathogenic) from this group of patients. The spectrum of aerobes in patients with VAP was similar to that reported in the literature. The organisms found in patients with AP was a reflection of the organisms likely to colonize the oropharynx. The use of antibiotics with anaerobic coverage may not be necessary in patients with suspected VAP and AP. Furthermore, penicillin G and clindamycin may not be the antibiotics of choice in patients with AP.

Section snippets

Materials and Methods

This study was conducted between June 1996 and August 1997 in the Medical and Surgical ICUs at St. Vincent Hospital, Worcester, MA. This study was approved by our Institutional Review Board. As both blind PSB sampling and mini-BAL are considered to be within the standard of care in our ICUs, the Institutional Review Board waived the need for informed consent. Patients were eligible for inclusion in this study if they had been mechanically ventilated for more than 48 h and were suspected to have

Results

During the study period, 185 paired specimens from 143 patients with suspected VAP and 25 paired specimens from 25 patients with AP were obtained. One patient with bacteriologically proven AP subsequently underwent blind PSB sampling/mini-BAL for suspected VAP (the cultures were negative). The clinical characteristics of both groups of patients are listed in Table 1. Blind PSB sampling and mini-BAL were performed within 24 h of the suspected episode of aspiration in the patients with AP. Blind

Discussion

Anaerobic bacteria are considered to be common pulmonary pathogens, and they are believed to play a major role in aspiration and nosocomial pneumonia.8, 23, 25, 32 These beliefs are based on a handful of studies conducted in the 1970s, when transtracheal aspiration was used for the collection of “uncontaminated” respiratory secretions19, 20, 21, 22, 32 Consequently, antimicrobial agents with anaerobic coverage have been recommended in patients with aspiration pneumonia and nosocomial pneumonia.7

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    For editorial comment see page 8.

    Supported by the St. Vincent Hospital Critical Care Research Fund. Theauthors have no financial involvement with any of the productsmentioned.

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