Streptococcal Infections

Streptococcus species are spherical gram positive bacteria that grow in chains or pairs. Streptococcus species are a major cause of human disease and are the etiologic organisms for many cases of meningitis, pneumonia, sepsis, endocarditis, strep throat, and necrotizing fasciitis. Streptococcus may cause disease in both immune competent and immune compromised hosts.

Streptococcus species are classified into alpha-he-molytic or beta-hemolytic groups based on how they break down red blood cells in vitro. Beta-hemolytic species are further classified according to Lansfield Groups A through O. Important human disease causing Alpha-hemolytic species include S. pneumoniae and S. viridans. Common human disease causing Beta-hemolytic species include Groups A and B.

S. pneumoniae is responsible for the majority of Streptococcal disease world wide and is a major cause of childhood and adult morbidity and mortality. Clinical manifestations of S. pneumoniae infections in neonates and young infants are serious and include pneumonia, meningitis, sepsis, bacteremia, [Page 1618]otitis media, abscesses, and bone and joint infections. Worldwide, it is the most common cause of bacterial pneumonia mortality and the most severe cause of bacterial meningitis.

Pneumococcal disease kills up to 1 percent of all children born in high mortality areas, and pneumococcal meningitis leaves approximately 50 percent of surviving children with life-long neurologic disabilities including deafness and seizures. According to the Centers for Disease Control, underlying co-morbidi-ties such as HIV infection, malnutrition, and sickle cell anemia significantly increase risk of invasive pneumococcal disease by up to 50 percent.

The World Health Organization estimates that more than 1.6 million people die of pneumococcal disease annually and that half of these deaths are of children under 5 years of age. The vast majority of these deaths occur in the developing world where there is currently limited access to potentially lifesaving pneumococcal vaccines.

Although common and often serious, pneumococcal disease is largely preventable by vaccination. The first pneumococcal conjugate vaccine was licensed in the United States in 2000. It includes purified capsular polysaccharide of the seven serotypes of S. pneumoniae most common in the United States. Studies have shown the conjugate vaccine to be safe and effective in highly effective; the vaccine's introduction has significantly decreased both infant and childhood pneumococcal disease due to vaccine serotypes.

Perhaps equally important, the vaccination of infants has resulted in ‘herd immunity’ and thus reduced transmission of the bacterium to adults thereby decreasing pneumococcal morbidity and mortality in the elderly. Trials in The Gambia and South African have demonstrated the vaccine to also be effective in developing world settings. While the pneumococcal conjugate vaccine is routinely given in most developed countries, its use remains poor in the developing world.

Other human disease causing Streptococcal species include S. viridans and Beta-hemolytic groups A, and B. S. viridans is a cause of endocarditis and dental abscesses. Group A Beta-hemolytic streptococcus, also known as S. pyogenes, is the cause of strep throat and scarlet fever. Group A streptococcus is frequently the cause of necrotizing faciitis (also known as flesh eating disease) which has high levels of morbidity and mortality even with prompt and appropriate treatment. Rheumatic fever is an immune mediated inflammatory disease triggered by Group A streptococcus. While no longer common in the developed world, it remains a leading cause of acquired heart disease worldwide. Group B streptococcus is a normal colonizer of the female reproductive tract and may cause neonatal sepsis and meningitis. Current recommendations by the CDC are for pregnant women to be tested for Group B streptococcus and given antibiotics during labor to reduce the risk of transmission to the infant.

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