What are pneumococcal infections?

Updated: Aug 27, 2018
  • Author: Claudia Antonieta Nieves Prado, MD; Chief Editor: John L Brusch, MD, FACP  more...
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S pneumoniae is a gram-positive, catalase-negative coccus that has remained an extremely important human bacterial pathogen since its initial recognition in the late 1800s. The term pneumococcus gained widespread use by the late 1880s, when it was recognized as the most common cause of bacterial lobar pneumonia.

Worldwide, S pneumoniae remains the most common bacterial cause of community-acquired pneumonia (CAP). However, a recent study involving state-of-the-art diagnostic techniques for bacterial, viral, and fungal infections indicated that a specific pathogen was detected in only 38% of CAP cases. Of these cases, one or more viruses were retrieved in 23% of cases and bacteria in 11%. A combination of bacterial and viral pathogens was seen in 3%. Fungal and mycobacterial organisms accounted for 1%. Human rhinoviruses were isolated in 9% of cases and influenza virus in 6%. S pneumoniae remained the most common cause of bacterial CAP, at 5% of patients. [4]

S pneumoniae is a common cause of bacterial meningitis, bacteremia, and otitis media. S pneumoniae infection is also an important cause of sinusitis, septic arthritis, osteomyelitis, peritonitis, and endocarditis. Worldwide in 2000, 14.5 million estimated episodes of invasive pneumococcal disease were reported in children younger than 5 years, which correlates to more than 800,000 estimated deaths (11% of all deaths in this age group). [5]

Pneumococcal vaccination, particularly routine childhood pneumococcal conjugate vaccine (PCV; introduced in the United States in 2000), has led to decreased rates of invasive pneumococcal infections (>90%) caused by pneumococcal serotypes covered by the vaccine, as well as overall decreased rates of invasive disease (45% overall; 75% in children < 5 years). In addition, herd immunity has led to decreased rates of disease in older children and adults. [6, 7, 8]

Surveillance data following introduction and widespread uptake of 7-valent PCV (PCV7) immunization showed an astounding reduction in invasive disease of 100% in children younger than 5 years in the United States (94% in all ages) when considering disease caused by serotypes contained in PCV7. [5]

Many subsequent studies have shown increased rates of invasive and noninvasive disease caused by serotypes not covered by the vaccine, including serotypes 15, 19A, and 33F. An analysis of over 700 cases of invasive disease in completely immunized children (PCV7) showed that 96% were due to nonvaccine serotypes. An additional 6 serotypes accounted for almost two thirds of invasive infections in this age group.

An analysis of 653 invasive pneumococcal infections in the Spanish population before and after the implementation of PCV7 immunization showed an increased incidence of invasive disease in the postvaccine period, which was primarily due to nonvaccine serotypes and was associated with higher rates of complications, such as septic shock. Similar studies in the United States and other European countries have shown similar results, introducing the concept of replacement disease and its effects.

Serotype 19A has received the most attention, not only because of increased disease rates associated with this serotype, but also owing to its association with increased drug resistance. Increased rates of invasive disease with such serotypes caused the overall rates of invasive disease to remain somewhat steady starting in 2002, although these rates remain greatly reduced from rates prior to introduction of the conjugate vaccine.

For these reasons, work on the development of a vaccine containing additional serotypes continued. A 13-valent PCV (PCV13) was approved by the US Food and Drug Administration (FDA) on February 24, 2010 with the hope that its induced T-cell–dependent immune response would have increased efficacy in children and elderly persons. This potential benefit has yet to be demonstrated in elderly individuals. [6, 9, 10, 11, 12, 13, 14, 15, 8, 16, 17, 18, 5, 19, 20]

The 23-valent polysaccharide vaccine is more effective in decreasing pneumococcal bacteremia than pneumonia. As a result, mortality rates have decreased. Ongoing surveillance will help determine the effects of widespread routine immunization with PCV13 and its expanded serotype coverage on pneumococcal disease in children and adults.

In January 2013, the FDA approved PCV13 for the prevention of invasive pneumococcal disease in children and adolescents between 6 and 17 years of age. [21] In February 2013, the CDC's Advisory Committee on Immunization Practices (ACIP) voted for the use of the vaccine in children with immunodeficiencies. The panel recommends routine use of a single dose of PCV13 for children aged 6-18 years who have an immunocompromising condition (eg, sickle cell disease or HIV infection) and have not previously received the vaccine. [22]

Despite an overall decreased incidence of otitis media caused by serotypes covered by vaccination since the introduction of the conjugate pneumococcal vaccine, an increase in rates of disease caused by serotypes not covered by the vaccine has occurred, as well as an increase in rates of diseases caused by vaccine-covered serotypes in incompletely immunized children. The incidence of otitis media caused by serotype 19F has remained steady. Overall health care utilization for otitis media has decreased, as has the incidence of recurrent otitis media in some populations and studies. [7, 23, 24, 25]

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