The genus Streptococcus is comprised of a wide variety of both commensal and pathogenic gram-positive bacteria which are found to exist a wide range of hosts, including humans, horses, pigs and cows. Within the host, streptococci are found to colonize the mucosal surfaces of the mouth, nares and pharynx. Under certain circumstances, they may also inhabit the skin, heart or muscle tissue.
Streptococcus pyogenes or Group A Streptococcus (GAS)
Group A Streptococcus is a bacterium often found in the throat and on the skin. People may carry group A streptococci in the throat or on the skin and have no symptoms of illness. Most GAS infections are relatively mild illnesses such as "strep throat," or impetigo. On rare occasions, these bacteria can cause other severe and even life-threatening diseases.
GAS is responsible for noninvasive disease (strep throat, cellulitis, impetigo); invasive disease (necrotizing fasciitis [NF], streptococcal toxic shock syndrome [STSS], bacteremia, pneumonia); nonsuppurative sequelae (rheumatic fever, post-streptococcal glomerulonephritis). STSS is a severe illness characterized by shock, multiorgan failure. NF presents with severe local pain, destruction of tissue. Rheumatic fever is a leading cause of acquired heart disease in young people worldwide.
These bacteria are spread through direct contact with mucus from the nose or throat of persons who are infected or through contact with infected wounds or sores on the skin. Ill persons, such as those who have strep throat or skin infections, are most likely to spread the infection. Persons who carry the bacteria but have no symptoms are much less contagious. Treating an infected person with an antibiotic for 24 hours or longer generally eliminates their ability to spread the bacteria. However, it is important to complete the entire course of antibiotics as prescribed. It is not likely that household items like plates, cups, or toys spread these bacteria.
Severe, sometimes life-threatening, GAS disease may occur when bacteria get into parts of the body where bacteria usually are not found, such as the blood, muscle, or the lungs. These infections are termed "invasive GAS disease." Two of the most severe, but least common, forms of invasive GAS disease are necrotizing fasciitis and Streptococcal Toxic Shock Syndrome. Necrotizing fasciitis (occasionally described by the media as "the flesh-eating bacteria") destroys muscles, fat, and skin tissue. Streptococcal toxic shock syndrome (STSS), causes blood pressure to drop rapidly and organs (e.g., kidney, liver, lungs) to fail. STSS is not the same as the "toxic shock syndrome" frequently associated with tampon usage. About 20% of patients with necrotizing fasciitis and more than half with STSS die. About 10%-15% of patients with other forms of invasive group A streptococcal disease die.
GAS infections can be treated with many different antibiotics. Early treatment may reduce the risk of death from invasive group A streptococcal disease. However, even the best medical care does not prevent death in every case. For those with very severe illness, supportive care in an intensive care unit may be needed. For persons with necrotizing fasciitis, surgery often is needed to remove damaged tissue.
Streptococcus agalactiae or Group B Streptococcus (GBS)
The rates of serious group B strep infections are much higher among newborns than among any other age group. Nonetheless, serious group B strep infections occur in other age groups in both men and women. Among non-pregnant adults, rates of serious disease range from 4.1 to 7.2 cases per 100,000 population.
GBS is responsible for in neonates: sepsis, pneumonia and meningitis. Infection in the first week of life is called "early-onset disease." In adults: sepsis and soft tissue infections. Pregnancy-related infections: sepsis, amnionitis, urinary tract infection, and stillbirth.
The rate of serious group B strep disease increases with age. The average age of cases in non-pregnant adults is about 60 years old. Most adult group B strep disease occurs in adults who have serious medical conditions. These include: diabetes mellitus; liver disease; history of stroke; history of cancer; or bed sores. Among the elderly, rates of serious group B strep disease are more common among residents of nursing facilities, and among bedridden hospitalized patients. Group B strep disease among non-pregnant adults may often be acquired after recent trauma, or after having certain invasive hospital procedures like surgery.
Resistance of Streptococcus pneumoniae to penicillin and other beta-lactams is increasing worldwide. The major mechanism of resistance involves the introduction of mutations in genes encoding penicillin-binding proteins. Selective pressure is thought to play an important role, and use of beta-lactam antibiotics has been implicated as a risk factor for infection and colonization.
Streptococcus pneumoniae is responsible for pneumonia, bacteremia, otitis media, meningitis, sinusitis, peritonitis and arthritis.
Until 2000, S. pneumoniae infections caused 100,000-135,000 hospitalizations for pneumonia, 6 million cases of otitis media, and 60,000 cases of invasive disease, including 3300 cases of meningitis. Incidence of sterile-site infections showed geographic variation from 21 to 33 cases per 100,000 population. Disease figures are now changing due to conjugate vaccine introduction.; in 2002, the rate of invasive disease was 13 cases per 100,000 in the United States.
For more than a century, Streptococcus pneumoniae has been known as the major bacterial pathogen in humans, causing substantial illness and death. Before 1967, this organism was uniformly susceptible to penicillin. In the early 1990s, pneumococcal isolates appeared that exhibited a high level of resistance to penicillin and other ß-lactam antibiotics. The widespread emergence of this resistance in many countries has become a major concern in recent years. The persistence of high antibiotic selective pressure in the community and international spread of epidemic or countrywide circulation of endemic multiresistant clones have substantially contributed to the crisis of resistance. This resistance has complicated treatment options and increased the likelihood of treatment failure.
The Asian region is one of the epicenters for pneumococcal resistance, and Taiwan has become the focus of pneumococcal resistance since 1996, particularly after several reports documented the alarmingly high prevalence among clinical isolates of resistance to ß-lactam antibiotics and macrolides. The Center for Disease Control under the Department of Health in Taiwan established an active surveillance program in 1998 to study the epidemiologic features of invasive pneumococcal diseases in Taiwan. Furthermore, a nationwide surveillance system for antimicrobial resistance involving 12 major teaching hospitals (Surveillance from Multicenter Antimicrobial Resistance in Taiwan [SMART]) has also tracked the trends of pneumococcal resistance annually since 2000.
The incidence of invasive infections caused by S. pneumoniae in Taiwan is still unknown, although several studies regarding invasive pneumococcal infections in adults and children have been reported. The overall mortality rate (42.5%) for elderly patients (>65 years of age) with invasive infections (bacteremia, pneumonia, pleural empyema, meningitis, septic arthritis, and peritonitis) was higher than the rates for patients 19-64 years of age (22.4%) and for children (8.1%). Some factors, such as the presence of serotype 3 strain, shock as initial presentation, and multilobar pneumonia, were significantly associated with death from invasive infections. Another report from central Taiwan indicated that the overall mortality rate for children with invasive pneumococcal infections was 20.3%, and in 53.3%, the infections progressed rapidly to death. Other studies found that 70% to 80% of adult patients with invasive pneumococcal disease had underlying diseases (malignancies, followed by congestive heart failure and diabetes mellitus). Patients with HIV infection or multiple myeloma in whom invasive pneumococcal infection developed were extremely rare. No significant difference was found in the mortality rates of patients with penicillin-susceptible (PSSP) and those with penicillin-nonsusceptible S. pneumoniae (PNSSP) infections.
The prevalence of this organism that causes community-acquired pneumonia or meningitis in adults or children is obscure. Several reports have indicated that this organism causes 19% to 33% of infections that results in bacterial meningitis in children. In one study of adult patients, 28% of the community-acquired bacterial meningitis were caused by S. pneumoniae, the highest proportion after that was by Klebsiella pneumoniae (33%). The incidence (cases per 100,000 emergency visits) of pneumococcal meningitis at National Taiwan University Hospital was 2.8 in 1997-1998. In other study, S. pneumoniae accounted for 21.8% of bacterial pathogens isolated from middle ear fluid from 243 children with acute otitis media.
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