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Pneumococcal pneumonia in adults

Thomas J Marrie, MD
Elaine I Tuomanen, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Sheila Bond, MD


Of the approximately four million cases of pneumonia each year in the United States, pneumococcus (Streptococcus pneumoniae) is the most common agent leading to hospitalization in all age groups [1]. (See "Epidemiology, pathogenesis, and microbiology of community-acquired pneumonia in adults".)

A general overview of pneumococcal pneumonia will be presented here. The epidemiology, microbiology, diagnosis, and treatment of community-acquired pneumonia are discussed separately. (See "Diagnostic approach to community-acquired pneumonia in adults" and "Epidemiology, pathogenesis, and microbiology of community-acquired pneumonia in adults" and "Treatment of community-acquired pneumonia in adults in the outpatient setting" and "Treatment of community-acquired pneumonia in adults who require hospitalization".)


Prevalence in community-acquired pneumonia — S. pneumoniae has traditionally been the most common cause of community-acquired pneumonia (CAP). In the preantibiotic era, S. pneumoniae was responsible for >75 percent of cases of pneumonia [2-4]. However, more recent studies have isolated the organism in only 5 to 15 percent of cases in the United States [5-9] but in a higher proportion of cases in some other countries [2,10,11]. Factors that are likely to have contributed to the decline in S. pneumoniae as a cause of CAP in the United States include the use of pneumococcal vaccines in adults, the universal use of pneumococcal conjugate vaccines in children (leading to herd immunity), and a reduction in cigarette smoking [2,12]. The impact of pneumococcal vaccination on the incidence of pneumonia is discussed in greater detail separately. (See "Pneumococcal vaccination in adults".)

It is important to note that the rate of isolation increases when more invasive methods are used for obtaining specimens, such as transtracheal aspiration, which eliminates contaminating oropharyngeal flora; this method was used in the past but is no longer used. It is believed that many culture-negative cases are caused by pneumococcus. One factor arguing for the predominance of S. pneumoniae as a cause of CAP is that, in patients with CAP who have positive blood cultures, 58 to 81 percent of bloodstream isolates are S. pneumoniae [1,13]; however, only 7 to 10 percent of patients with CAP have positive blood cultures [1,6,13]. One group has estimated that, for every case of bacteremic pneumococcal pneumonia, there are at least three additional cases of nonbacteremic pneumococcal pneumonia [14].

Risk factors

Influenza infection — Influenza infection greatly predisposes to secondary pneumococcal pneumonia [15]. This is discussed in detail separately. (See "Clinical manifestations of seasonal influenza in adults", section on 'Secondary bacterial pneumonia'.)

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Literature review current through: Nov 2017. | This topic last updated: May 30, 2017.
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