Microbiological profile and multidrug resistant bacteria in pneumonia

Background

Currently accepted classifications of pneumonia include community acquired pneumonia (CAP), healthcare-associated pneumonia (HCAP), hospital-acquired pneumonia (HAP), and ventilator-associated pneumonia (VAP). Previous studies have shown a high rate of patients with HCAP or HAP caused by multidrug-resistant bacteria (MDR). Our aim was to determine the differences in etiology and antibiotic-resistant bacteria between CAP, HCAP and HAP groups.

Methods

We performed a retrospective study in which we included patients over 18 years old, with culture-positive pneumonia, between 2008 and 2011, from 3 clinical hospitals. The patients were classified as having CAP, HCAP or HAP. We recorded the bacteriologic results for the following samples: blood culture, sputum, bronchial aspirate, bronchoalveolar lavage. The statistical analysis was carried out using Graph Pad Prism 5.

Results

A total of 340 patients were recorded (160 with CAP, 39 with HCAP and 141 with HAP). Streptococcus pneumoniae and Haemophilus influenzae were seen more frequently in CAP (33%, 14.4%) than in HCAP or HAP (1.4%, 0%; p<0.0001). The most common pathogens in HAP were MRSA (27.7%), Acinetobacter spp. (26.2%), Klebsiella pneumoniae (19%). Compared to the HCAP, Acinetobacter spp. and MRSA were significantly associated with HAP (OR 54.8, p<0.0001, LR 3.9). Compared to the HAP P aeruginosa and E coli were more common in HCAP (36%, p 0.04, OR 2; respectively 23%, p 0.001, OR 7). Among Gram-negative bacilli, resistance to ceftazidime was higher (86%) and significantly associated with HAP (OR 14.3, p<0.0001, LR 2.7). The extended-spectrum β-lactamase-producing Enterobacteriaceae, were more frequent in HAP (67.7%). However, no differences were found regarding ESBL producing Enterobacteriaceae between HAP and HCAP (p=0.06). MDR bacteria, including MRSA and gram-negative bacilli, were identified more frequently in HAP versus HCAP (78.7% vs. 12.8%; p<0.0001, OR 25, LR 6).

Conclusion

S pneumoniae was the main causative pathogen in CAP. Despite the higher frequency of P aeruginosa in the HCAP group, the MDR bacteria were associated with the HAP group. Our results reveal important differences between HAP and HCAP concerning the etiology and antibiotic resistance patterns.