Pneumococcus

Responsible for the disease is Streptococcus pneumoniae, a Gram-positive bacterium, also known as pneumococcus, which can survive in both aerobic and anaerobic conditions (i.e., in the presence or absence of oxygen).
Pasteur and Sternberg first isolated S. pneumoniae from saliva in 1881. Currently, there are several reports on the exact number of identified serotypes of S. pneumoniae, which are at least 97.

Transmission occurs through the air via droplets emitted by sneezing, coughing or simply talking, or by indirect contact with contaminated material.
The severity of pneumococcal disease has led to multiple studies investigating the mode of transmission of S. pneumoniae. The nasopharynx has been classified as the main reservoir. This is because the nasopharynx of hosts is colonized often without any symptoms. After colonization, the spread of the disease depends on carriers coming into close contact with healthy individuals within the community.

Pneumococcal diseases occur worldwide and are most prevalent in young children, the elderly, and immunocompromised individuals. S. pneumoniae causes many pneumococcal diseases such as meningitis, bacteremia, pneumonia, acute otitis media, and sinusitis and causes about 40,000 fatal pneumococcal infections per year in the United States.

After an incubation period that can range from 1 to 3 days, depending on the type of infection, the first symptoms occur.

Pneumococcal disease can be classified into two broad categories;

• Invasive infections: affecting vital organs or blood with very serious consequences, for example; meningitis, sepsis, pneumonia, pneumococcal bacteremia, septic arthritis and septicemia.
• Non-invasive infections: these infections are generally easy to resolve without causing permanent damage e.g.; otitis media, sinusitis and conjunctivitis.

The symptoms of a Streptococcus Pneumoniae infection take on different aspects depending on the body site affected. The most common infections that this bacterium causes are pneumonia, otitis media, and meningitis. Pneumococcal pneumonia is a form of inflammation of the lungs. The onset of symptoms is typically abrupt with high fever, chills, tachypnea (increased respiratory rate), cough accompanied by the emission of russet-colored sputum, wheezing, and chest pain generally localized to one side, referred to as lobar pneumonia. In about 40% of cases, fluid forms between the layers lining the lungs, causing pleural effusion, which contributes to chest pain and difficulty breathing. Bacterial meningitis is another disease caused by pneumococcus, which is very serious. It is an inflammation of the meninges, which are the membranes lining the brain. It manifests, on average after an incubation period of 7 days, with an abrupt onset of; high fever, headache, convulsion, chills, neck stiffness and jet vomiting. Pneumococcal meningitis can give rise term rather severe complications such as; hearing loss (the most common complication), seizures, memory loss, learning disabilities, and vision loss. Otitis of the middle ear occurs predominantly in childhood, with a rate of about 30%-40%. It causes ear pain accompanied by redness and eversion of the eardrum membrane, and pus may form behind the eardrum.

Currently, there are several methods used in diagnosing pneumococcal disease.
Traditionally, diagnosis begins with a clinical examination. More specifically, for pneumonia, based on the results of the objective examination, a chest X-ray can be performed to examine the lungs and monitor inflammation to confirm the presence of infection.
Bacterial cultures and Gram staining tests using body fluids are important to determine the strain of bacteria and confirm their identity. Currently, clinicians are investigating other means of diagnosing pneumococcal infections due to poor sample yield and quality when conducting cultures. This process also depends on bacterial growth, which can take a long time.

Treatment of pneumococcal infections relies on antibiotic therapy to reduce the bacterial load and support vital functions.
Treatment can work by killing the bacteria or by hindering their growth. The first antibiotic created was penicillin, and antibiotics have been widely used ever since. However, improper use of antibiotics can cause bacteria to become resistant. Currently, penicillin-resistant strains have spread worldwide, and pneumococcus is also resistant to other types of antibiotics: erythromycin, tetracycline and chloramphenicol. In 2013, the CDC estimated that about 30 percent of pneumococcal cases were due to antibiotic resistance to one or more antibiotics.

The main mode of prevention of pneumococcal infections is vaccination. There are mainly two types of vaccine:
Pneumococcal polysaccharide vaccine 23 (PPSV23) uses purified capsular polysaccharides and is routinely given to adults aged 65 years and older. It protects against 23 serotypes of S. pneumoniae and is effective in 50-70% of cases in adults. PPSV23 provides T-cell-independent immunity and requires revaccination 5 years after the first vaccination because immunity is transient.
Pneumococcal conjugate vaccine (PCV13). This, was developed after noticing the low efficacy and poor immunogenicity of PPSV23 in infants and young children. In the conjugate vaccine, purified polysaccharides covalently conjugated with a carrier protein. This causes a T-cell-dependent response that provides mucosal immunity and immunological memory in children that is stronger in quality and duration.
At present, children and adults who are at high risk of pneumococcal disease and have pre-existing conditions are given the prevention strategy with PCV13 first, followed by PPSV23.