New Antibiotics for Community-Acquired Pneumonia

Marin H. Kollef; Kevin D. Betthauser


Curr Opin Infect Dis. 2019;32(2):169-175. 

In This Article

Pathogens Associated With Community-acquired Pneumonia

The cause of CAP is most often described as bacterial with Streptococcus pneumoniae being the most common bacterial pathogen followed by Haemophilus influenzae, Staphylococcus aureus, Mycoplasma pneumoniae, group A streptococci, Legionella spp., Chlamydophila, and Moraxella catarrhalis.[11] However, the advent of molecular diagnostic techniques has identified respiratory viruses as an increasingly important cause of CAP in various regions. A recent US review found that among 2259 patients who had radiographic evidence of pneumonia and specimens available for both bacterial and viral testing, a pathogen was detected in 853 (38%), one or more viruses in 530 (23%), bacteria in 247 (11%), bacterial and viral pathogens in 59 (3%), and a fungal or mycobacterial pathogen in 17 (1%)[5] (Table 1). Similarly, a prospective study from Spain of 4431 patients with CAP identified a microbiologic cause in 40% with Strep. pneumoniae being most common followed by respiratory viruses, atypical bacterial pathogens, Staph. aureus, and H. influenzae.[12] It is also important to be aware of local problem pathogens associated with CAP including Burkholderia pseudomallei in the Asia-Pacific region, Coxiella burnetti in Nova Scotia, Canada, and the Basque region of Spain, and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) in the Middle East.

The cause of pneumonia, including CAP, can also vary according to the patient population examined and their underlying comorbidities. For example, a recent study of pneumonia complicating patients with stroke found that the majority of pneumonias occurred within 1 week of the onset of stroke (78%) and the predominant pathogens were Gram-negative bacteria (38%) and Gram-positive cocci (16%), including Enterobacteriaceae, Staph. aureus(10%), Pseudomonas aeruginosa (6%), Acinetobacter baumanii (5%), and Strep. pneumoniae (4%).[13] However, it is likely that this population included patients with aspiration pneumonia and hospital-acquired pneumonia (HAP) depending on the timing of the onset of infection. Among patients with chronic obstructive pulmonary disease, the cause of CAP also differs with Strep. pneumoniae predominating followed by respiratory viruses, P. aeruginosa, atypical bacterial pathogens, and H. influenzae in descending order.[14] Clinicians should also be aware that patients admitted to the hospital with pneumonia may possess specific risk factors (recent intravenous antibiotics, admission from a long-term care facility) predisposing them to infection with nosocomial bacterial pathogens, including P. aeruginosa and methicillin-resistant Staph. aureus (MRSA).[15] This type of pneumonia called healthcare-associated pneumonia (HCAP), despite the origin of these individuals from outside the hospital setting, has been controversial in terms of its classification, empiric treatment, and frequent failure of initial antimicrobial treatment.[16,17]