Pneumococci

Diplococci in the blood of rabbits were first described in the late 19th century by Louis Pasteur (Paris) and Georg Sternberg (American army doctor). In the years 1884-1886, several authors independently of each other succeeded in proving the so-called Diplokokkus pneumoniae.

Pneumococci are gram-positive (turning blue when Gram stain) bacteria that belong to the group of streptococci (chain cocci). However, the chain here consists of only two links. These are diplococci. Streptococcus pneumoniae has no Lancefield group antigens. However, the antigenic structure of the polysaccharide capsule allows a subdivision into 91 serovars. The polysaccharide capsule is the most important pathogenicity factor and has an antiphagocytic effect.

Worldwide, pneumococcal diseases cause the death of about two million people per year.

Risk factors for disease are:

• age (children and the elderly have a significantly higher incidence)
• congenital and acquired immunodeficiencies
• chronic diseases (e.g. alcoholism, chronic heart or lung diseases, splenectomy)

The Standing Vaccination Commission (STIKO) recommends that all adults over the age of 65 should be vaccinated in general. The vaccine PPSV23 should be used, as it protects against 23 of a total of more than 90 serotypes. A general booster is not recommended for healthy persons and should be decided by the treating physician in each individual case.

However, in the above-mentioned persons with an increased risk of severe pneumococcal disease, a booster is recommended after at least six years (STIKO with reference to the technical information on PPSV23). Considerable side-effects are to be expected if a booster is given before the 6-year period has expired.

For immunocompromised patients and for patients with chronic diseases such as asthma, COPD, emphysema, seizure disorders, cerebral palsy and diabetes mellitus a first sequential vaccination with PCV13 is recommended. Only after 6 to 12 months vaccination with PPSV23 should be given.

Transmission occurs from person to person by droplet infection and in about 15% by haematogenous spread. In most cases, however, the infection is endogenous.

In infants, pneumococci are found in the mucous membranes of the nasopharynx in up to 60 %; in adults, they are detectable in only about 10 %. However, the number increases again with age due to the weaker immune system. In adults without contact with small children, diplococci are found in the nasopharynx in only 5 %.

Pneumococci are not obligatory pathogenic, because normally an intact immune system prevents the disease. However, if disease does occur, it matters a great deal whether encapsulated or unencapsulated strains of bacteria are involved. The unencapsulated strains are rarely pathogenic, but they adhere more readily to weakened or damaged mucosal epithelia. The encapsulated strains, on the other hand, exhibit much higher virulence.

The capsular polysaccharide of pneumococci is very variable, so that more than 90 serotypes (serovars) can be distinguished. These serotypes play a major role in a new infection with pneumococci (no cross-immunity!) and in pneumococcal vaccination.

Transmission occurs from person to person by droplet infection and in about 15% by haematogenous spread. In most cases, however, the infection is endogenous. In infants, pneumococci are found in the mucous membranes of the nasopharynx in up to 60 %; in adults, they are detectable in only about 10 %. However, the number increases again with age due to the weaker immune system. In adults without contact with small children, diplococci are found in the nasopharynx in only 5 %. Pneumococci are not obligatory pathogenic, because normally an intact immune system prevents the disease. However, if disease does occur, it matters a great deal whether encapsulated or unencapsulated strains of bacteria are involved. The unencapsulated strains are rarely pathogenic, but they adhere more readily to weakened or damaged mucosal epithelia. The encapsulated strains, on the other hand, exhibit much higher virulence.

The capsular polysaccharide of pneumococci is very variable, so that we distinguish more than 90 serotypes (serovars). These serotypes play a major role in the re-infection with pneumococci (no cross-immunity!) and in pneumococcal vaccination.

Epidemiology: Worldwide, pneumococcal disease kills about two million people a year. Risk factors for disease are:

• age (children and the elderly have a significantly higher incidence)
• congenital and acquired immunodeficiencies
• chronic diseases (e.g. alcoholism, chronic heart or lung diseases, splenectomy).

Pneumococci can cause a variety of diseases:

• Pneumonia (pathogen in approx. 40 - 50 % of cases pneumococci)
• Otitis media (pneumococcus in approx. 25 % of cases)
• Meningitis (pneumococcus in approx. 60 % of cases)
• Sinusitis (pathogen in approx. 40 % of cases pneumococci)
• Rhinitis
• Sepsis (pathogen in just under 10 % of cases pneumococci)
• Conjunctivitis
• Ulcus serpens corneae
• OPSI(Overwhelming postsplenectomy infection): In the elderly and splenectomized patients, pneumococcal sepsis often occurs with a high mortality rate (>30%) due to the loss of this "draining lymphatic organ".

Against pneumococcal infections there is active immunization. The protective effect is about 70%. The vaccination can be administered both s.c.and i.m.administered. A vaccine against pneumococci was first developed in 1945 with four capsular antigens. In the 1970s, a vaccine with 14 antigens was added. The current variant with 23 vaccine strains (23-valent polysaccharide vaccine PPSV23) was developed in 1983. This contains antigens from 23 different pneumococcal types, which in turn are responsible for 90 percent of pneumococcal disease in adults. In 2001, the conjugate vaccine PCV13 appeared on the market.

Nowadays we distinguish two different vaccines for adults:

• 23-valent polysaccharide vaccine PPSV23 (trade name Pneumovax® 23)
• 13-valent conjugate vaccine PCV13 (trade name Prevenar® 13).

Differences between the vaccines: Although PPSV 23 includes more serotypes than PCV13, PPSV 23 stimulates only B cells and not T cells. Consequently, no immunological memory can be established. This then leads to depletion of the B cell pool. Especially in elderly people, but also in immunosuppressed individuals, specific new naïve B cells can only form very slowly, which has been demonstrated in several studies by reduced antibody formation. This effect is called hyporesponsiveness. Only 10 years after the first vaccination this phenomenon is no longer detectable.

Conjugate vacc ines contain fewer serotypes, but an additional T-cell response with the formation of memory cells is achieved by binding the capsular polysaccharides to highly immunogenic carrier proteins. Furthermore, the formation of so-called secretory antibodies occurs, which in turn cause a protection of the mucosal mucosa.

According to the Infection Protection Act, the detection of pneumococci is not reportable in Germany.

However, some federal states have introduced a reporting requirement by state ordinance. These include:

• Brandenburg
• Mecklenburg-Western Pomerania
• Saxony
• Saxony-Anhalt (special status see below)

In Brandenburg, Mecklenburg-Western Pomerania and Saxony, there is an obligation to report by name in accordance with Section 7(1) of the Infection Protection Act in the event of direct or indirect evidence of Streptococcus pneumoniae.

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Pneumovax® should be used preferentially for the following groups of people when availability is limited:

• Patients with congenital or acquired immunodeficiencies or immunosuppression: to complete sequential vaccination.
• Seniors over 70 years of age
• Patients with chronic diseases of the heart or the respiratory organs.

The STIKO points out that due to the broader coverage of pneumococcal serotypes, the vaccine cannot be replaced by another lower-valent pneumococcal vaccine.

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