Streptococcus Pneumoniae : Clinical Features, Pneumococcal Disease in Children, Laboratory Diagnosis and Medical Management
Streptococcus pneumoniae bacteria are lancet-shaped, gram-positive, facultative anaerobic organisms. They are typically observed in pairs (diplococci) but may also occur singularly or in short chains. Most pneumococci are encapsulated, their surfaces composed of complex polysaccharides. Capsular polysaccharides are one determinant of the pathogenicity of the organism. They are antigenic and form the basis for classifying pneumococci by serotypes.
Ninety-two serotypes have been documented as of 2011, based on their reaction with type-specific antisera. Type-specific antibody to capsular polysaccharide is protective. These antibodies and complement interact to opsonize pneumococci, which facilitates phagocytosis and clearance of the organism. Antibodies to some pneumococcal capsular polysaccharides may cross-react with related types as well as with other bacteria, providing protection against additional serotypes.
Most S. pneumoniae serotypes have been shown to cause serious disease, but only a few serotypes produce the majority of pneumococcal infections. The 10 most common serotypes are estimated to account for about 62% of invasive disease worldwide. The ranking and serotype prevalence differ by patient age group and geographic area. In the United States, prior to widespread use of 7-valent pneumococcal conjugate vaccine (PCV7), the seven most common serotypes isolated from blood or cerebrospinal fluid (CSF) of children younger than 5 years of age accounted for 80% of infections.
These seven serotypes accounted for only about 50% of isolates from older children and adults.
Pneumococci are common inhabitants of the respiratory tract and may be isolated from the nasopharynx of 5% to 90% of healthy persons. Rates of asymptomatic carriage vary with age, environment, and the presence of upper respiratory infections. Among school-aged children, 20%–60% may be colonized. Only 5%–10% of adults without children are colonized although, on military installations, as many as 50%–60% of service personnel may be colonized. The duration of carriage varies and is generally longer in children than adults. In addition, the relationship of carriage to the development of natural immunity is poorly understood.
Clinical Features
The major clinical syndromes of pneumococcal disease are pneumonia, bacteremia, and meningitis.
Pneumococcal pneumonia is the most common clinical presentation of pneumococcal disease among adults. The incubation period of pneumococcal pneumonia is short, about 1 to 3 days. Symptoms generally include an abrupt onset of fever and chills or rigors. Classically there is a single rigor, and repeated shaking chills are uncommon. Other common symptoms include pleuritic chest pain, cough productive of mucopurulent, rusty sputum, dyspnea (shortness of breath), tachypnea (rapid breathing), hypoxia (poor oxygenation), tachycardia (rapid heart rate), malaise, and weakness. Nausea, vomiting, and headaches occur less frequently.
Approximately 400,000 hospitalizations from pneumococcal pneumonia are estimated to occur annually in the United States. Pneumococci account for up to 36% of adult community-acquired pneumonia. Pneumococcal pneumonia has been demonstrated to complicate influenza infection. About 25-30% of patients with pneumococcal pneumonia also experience pneumococcal bacteremia.
The case-fatality rate is 5%–7% and may be much higher among elderly persons. Other complications of pneumococcal pneumonia include empyema (i.e., infection of the pleural space), pericarditis (inflammation of the sac surrounding the heart), and endobronchial obstruction, with atelectasis and lung abscess formation.
More than 12,000 cases of pneumococcal bacteremia without pneumonia occur each year. The overall case-fatality rate for bacteremia is about 20% but may be as high as 60% among elderly patients. Patients with asplenia who develop bacteremia may experience a fulminant clinical course.
Pneumococci cause over 50% of all cases of bacterial meningitis in the United States. An estimated 3,000 to 6,000 cases of pneumococcal meningitis occur each year. Some patients with pneumococcal meningitis also have pneumonia. The clinical symptoms, cerebrospinal fluid (CSF) profile and neurologic complications are similar to other forms of purulent bacterial meningitis. Symptoms may include headache, lethargy, vomiting, irritability, fever, nuchal rigidity, cranial nerve signs, seizures and coma. The case-fatality rate of pneumococcal meningitis is about 8% among children and 22% among adults. Neurologic sequelae are common among survivors.
Adults with certain medical conditions are at highest risk for invasive pneumococcal disease. For adults aged 18-64 years with hematologic cancer, the rate of invasive pneumococcal disease in 2010 was 186 per 100,000, and for persons with human immunodeficiency virus (HIV) the rate was 173 per 100,000. Other conditions that place adults at highest risk for invasive pneumococcal disease include other immunocompromising conditions, either from disease or drugs, functional or anatomic asplenia, and renal disease. Other conditions that increase the risk of invasive pneumococcal disease include chronic heart disease, pulmonary disease (including asthma in adults), liver disease, smoking cigarettes (in adults) CSF leak, and having a cochlear implant.
Read Also : Bordetella Pertussis : Clinical Features, Complications, Laboratory Diagnosis, Medical Management
Pneumococcal Disease in Children
Bacteremia without a known site of infection is the most common invasive clinical presentation of pneumococcal infection among children 2 years of age and younger, accounting for approximately 70% of invasive disease in this age group. Bacteremic pneumonia accounts for 12%–16% of invasive pneumococcal disease among children 2 years of age and younger. With the decline of invasive Hib disease, S. pneumoniae has become the leading cause of bacterial meningitis among children younger than 5 years of age in the United States. Before routine use of pneumococcal conjugate vaccine, children younger than 1 year had the highest rates of pneumococcal meningitis, approximately 10 cases per 100,000 population.
Pneumococci are a common cause of acute otitis media and are detected in 28%–55% of middle ear aspirates. By age 12 months, more than 60% of children have had at least one episode of acute otitis media. Middle ear infections are the most frequent reasons for pediatric office visits in the United States, resulting in more than 20 million visits annually. Complications of pneumococcal otitis media may include mastoiditis and meningitis.
Before routine use of pneumococcal conjugate vaccine, the burden of pneumococcal disease among children younger than 5 years of age was significant. An estimated 17,000 cases of invasive disease occurred each year, of which 13,000 were bacteremia without a known site of infection and about 700 were meningitis. An estimated 200 children died every year as a result of invasive pneumococcal disease. Although not considered invasive disease, an estimated 5 million cases of acute otitis media occured each year among children younger than 5 years of age.
Children with functional or anatomic asplenia, particularly those with sickle cell disease, and children with immune compromise including human immunodeficiency virus (HIV) infection are at very high risk for invasive disease, with rates in some studies more than 50 times higher than those among children of the same age without these conditions (i.e., incidence rates of 5,000–9,000 per 100,000 population). Rates are also increased among children of certain racial and ethnic groups, including Alaska Natives, African Americans, and certain American Indian groups (Navajo and White Mountain Apache).
The reason for this increased risk by race and ethnicity is not known with certainty but was also noted for invasive Haemophilus influenzae infection (also an encapsulated bacterium). Attendance at a child care center has also been shown to increase the risk of invasive pneumococcal disease and acute otitis media 2–3-fold among children younger than 59 months of age. Children with cochlear implants are at increased risk for pneumococcal meningitis.
Laboratory Diagnosis
A definitive diagnosis of infection with S. pneumoniae generally relies on isolation of the organism from blood or other normally sterile body sites. Tests are also available to detect capsular polysaccharide antigen in body fluids.
The appearance of lancet-shaped diplococci on Gram stain is suggestive of pneumococcal infection, but interpretation of stained sputum specimens may be difficult because of the presence of normal nasopharyngeal bacteria. The suggested criteria for obtaining a diagnosis of pneumococcal pneumonia using gram-stained sputum includes more than 25 white blood cells and fewer than 10 epithelial cells per high-power field, and a predominance of gram-positive diplococci.
A urinary antigen test based on an immunochromatographic membrane technique to detect the C-polysaccharide antigen of Streptococcus pneumoniae as a cause of community-acquired pneumonia among adults is commercially available and has been cleared by FDA. The test is rapid and simple to use, has a reasonable specificity in adults, and has the ability to detect pneumococcal pneumonia after antibiotic therapy has been started.
Medical Management
Resistance to penicillin and other antibiotics was previously very common. However, following introduction of PCV7, antibiotic resistance declined and then began to increase again. Then, in 2008, the definition of penicillin resistance was changed such that a much larger proportion of pneumococci are now considered susceptible to penicillin. The revised susceptibility breakpoints for S. pneumoniae, published by the Clinical and Laboratory Standards Institute (CLSI) in January 2008, were the result of a reevaluation that showed clinical response to penicillin was being preserved in clinical studies of pneumococcal infection, despite reduced susceptibility response in vitro.
Guidelines for treatment of meningitis and pneumonia are available from professional societies.
Epidemiology
Occurrence
Pneumococcal disease occurs throughout the world.
Reservoir
S. pneumoniae is a human pathogen. The reservoir for pneumococci is the nasopharynx of asymptomatic humans. There is no animal or insect vector.
Transmission
Transmission of S. pneumoniae occurs as the result of direct person-to-person contact via respiratory droplets and by autoinoculation in persons carrying the bacteria in their upper respiratory tract.
Different pneumococcal serotypes have different propensities for causing asymptomatic colonization, otitis media, meningitis, and pneumonia. The spread of the organism within a family or household is influenced by such factors as household crowding and viral respiratory infections.
Temporal Pattern
Pneumococcal infections are more common during the winter and in early spring when respiratory diseases are more prevalent.
Communicability
The period of communicability for pneumococcal disease is unknown, but presumably transmission can occur as long as the organism appears in respiratory secretions.
Streptococcus Pneumoniae : Clinical Features,Streptococcus Pneumoniae : Clinical Features, Laboratory Diagnosis and Medical Management,Streptococcus Pneumoniae : Clinical FeaturesStreptococcus Pneumoniae : Clinical Features,Laboratory Diagnosis and Medical Management
0 comments:
Post a Comment