Pneumococcus

Pneumococcus or Streptococcus pneumoniae is a widespread bacteria that is commonly found in the upper respiratory tract (nose and throat) of healthy children and adults.

It is estimated that 30-70% of healthy people, children more frequently than adults, are carriers of Streptococcus pneumoniae. In hosts with normal immunity, Pneumococcus is found in the airways and causes no disturbance; in most cases, therefore, the carrier does not know that he is harbouring this germ. More than 93 different types (serotypes) of Pneumococcus are known; these differ for the type of capsule they are contained in. The capsule, a shell consisting of "sugars" called polysaccharides, makes streptococcus resistant to opsonisation and phagocytosis and is considered the main pneumococcal factor for pathogenicity. [1]

Transmission route

Pneumococcus spreads easily from subject to subject; transmission is airborne via the droplets of saliva emitted by sneezing, coughing or simply talking or through the exchange of contaminated material in the respiratory secretions of carriers. Cases of disease occur mainly in the winter period, when colds and flu are frequent, predisposing its onset. Infections are sporadic; epidemics are uncommon but can occur in close communities such as kindergartens, schools and other institutions.

Symptoms and complications

The onset of symptoms in people with Pneumococcus is linked to conditions that alter the integrity of the mucous membrane of the respiratory tract, such as concomitant viral infections, or diseases that reduce the efficiency of the immune system. The infection usually manifests with symptoms affecting the upper respiratory tract, where this bacterium is generally found, giving clinical pictures of otitis and sinusitis. When the germs reproduce in parts of the body where they are not normally present, such as the blood, liquor (transparent liquid that surrounds the brain and spinal cord) or the lungs, the disease manifests in a severe form, with pictures of, respectively, bacteremia, meningitis and pneumonia. These serious forms of infection, called invasive forms, can progress to sepsis, a condition with very high mortality characterised by the dissemination of bacteria in the bloodstream.

Those most at risk of developing a serious infection are children, especially in the first two years of life, and the elderly (typically, those over sixty-five are considered to be at greater risk). People who suffer from diseases that compromise the immune system, those with chronic illnesses (such as diabetes, heart disease, liver disease, kidney failure, blood diseases) and those who have had their spleen removed are also considered at risk. [2-3]

Severe forms of pneumococcal infection are even more threatening when we consider that over time Pneumococcus has developed resistance to some widely used antibiotics. [4]

1] J.N. Weiser et al., 2018. Streptococcus pneumoniae: transmission, colonization and invasion. Nature Reviews Microbiology, 16(6), 355–367
1] J.N. Weiser et al., 2018. Streptococcus pneumoniae: transmission, colonization and invasion. Nature Reviews Microbiology, 16(6), 355–367

The onset of symptoms in people with Pneumococcus is linked to conditions that alter the integrity of the mucous membrane of the respiratory tract, such as concomitant viral infections, or diseases that reduce the efficiency of the immune system. The infection usually manifests with symptoms affecting the upper respiratory tract, where this bacterium is generally found, giving clinical pictures of otitis and sinusitis. When the germs reproduce in parts of the body where they are not normally present, such as the blood, liquor (transparent liquid that surrounds the brain and spinal cord) or the lungs, the disease manifests in a severe form, with pictures of, respectively, bacteremia, meningitis and pneumonia. These serious forms of infection, called invasive forms, can progress to sepsis, a condition with very high mortality characterised by the dissemination of bacteria in the bloodstream.

Those most at risk of developing a serious infection are children, especially in the first two years of life, and the elderly (typically, those over sixty-five are considered to be at greater risk). People who suffer from diseases that compromise the immune system, those with chronic illnesses (such as diabetes, heart disease, liver disease, kidney failure, blood diseases) and those who have had their spleen removed are also considered at risk. [2-3]

Severe forms of pneumococcal infection are even more threatening when we consider that over time Pneumococcus has developed resistance to some widely used antibiotics. [4]

Impact on the population

Pneumococcus is the microorganism most frequently responsible for cases of acute otitis media in children; pneumococcal infection is above all the main cause of bacterial meningitis and bacterial pneumonia contracted in the community (an estimated 2/3 of the cases of infection).

In Italy in 2017, the active system of surveillance for invasive bacterial diseases reported 1,703 cases of invasive pneumococcal disease. In the same period of 2016, 1,531 were reported and in 2015 for the same period there were 1,259. Overall, the incidence of pneumococcal invasive diseases in Italy in the reference period was 2.07/100,000 inhabitants in 2015 and 2.81/100,000 inhabitants in 2017, lower than the European average of 6.2/100,000 inhabitants reported in 2017. [5]

Pneumococcus is the organism responsible most frequently for acute otitis media in children; pneumococcal infection is above all the first cause of bacterial meningitis and bacterial pneumonia contracted in the community (it is estimated to be involved in 2/3 of the cases of infection).

The system of surveillance of invasive bacterial diseases, active in our country, reported in 2017, 1703 cases of invasive pneumococcal disease. In the same period of 2016, 1531 and 2015 were reported, 1259. Overall, pneumococcal invasive diseases in Italy in the reference period had an incidence between 2.07 / 100 000 inhabitants in 2015 and 2.81 / 100 000 inhabitants in 2017, lower than the European average of 6.2 / 100 000 inhabitants reported in 2017. [5]

Reporting rate of invasive pneumococcal bacterial disease in Italy (number of reported cases per 100,000 population) per Region, 2017
Reporting rate of invasive pneumococcal bacterial disease in Italy (number of reported cases per 100,000 population) per Region, 2017

From 2015 onwards, the number of cases of invasive pneumococcal disease reported has steadily increased, following a typical seasonal pattern. Based on the available data, it is believed that this increase may be due mainly to an increase in diagnostic sensitivity and a greater attention to the problem. [5]

The incidence of invasive pneumococcal disease is highest in the over-64s (7.3 cases/100,000 inhabitants in 2017) and children under one year of age (5.6 cases/100,000 inhabitants in 2017). An upward trend is confirmed compared to previous years, particularly among adults over the age of 65. [5]

In children, meningitis is the most frequent manifestation of severe Pneumococcal infection, while the other age groups (adults and the elderly) are more often affected by pneumonia and bacteremia. Invasive infections are also the most frequent cause of hospitalisation in children and adults. Data provided by WHO in relation to Europe and the United States ascribe 30-50% of pneumonia cases requiring hospitalisation due to their severity to Pneumococcus; this percentage is higher in children, given that some estimates attribute almost 80% of lobar pneumonia (inflammation affecting a large portion of the lung lobe) to pneumococcus.

In the 2015-2017 period, the most frequent presentations of invasive pneumococcal diseases in Italy were sepsis/bacteremia which were not associated with another clinical picture (34-38% of cases) and sepsis/bacteremia-associated pneumonia (31-35% of cases), followed by meningitis, whether or not associated with sepsis/bacteremia, (28-29% of cases). Clinical pictures of pneumonia, pleurisy and peritonitis isolated from sterile sites, apart from blood, have been rare. [5]

Comparing the Italian data with the latest European Centre for Infectious Disease Prevention and Control (ECDC) report, in which clinical presentation was known in 34% of cases (8,055), sepsis was reported in 2,848 cases (35%), bacterial pneumonia in 3,414 (42%), meningitis in 1,499 (19%), meningitis and septicemia in 74 (1%) while a further 220 cases (3%) presented other clinical manifestations. The most common clinical presentation in children under the age of one and between 5-14 years was meningitis; in children aged 1-4, sepsis and bacterial pneumonia with the same frequency, and in those aged 15 and over, bacterial pneumonia was more common. [6]

Information on the serotype was identified for 57% of the cases reported in 2015, for 64% of the cases reported in 2016 and for 60% of the cases reported in 2017. Although there has been progress compared to the years prior to 2015, such a proportion is still not optimal. This is due to the differing levels of participation of the Regions in the surveillance and to the number of incomplete serotypings reported which were therefore unusable for the purposes of surveillance. [5] In this regard, it is very important to promote the use of data typing and sharing, in order to establish the exact proportion of vaccine-preventable cases and to detect any increase in serotypes not present in the vaccine currently used (known as the "replacement of serotypes"). At the European level, information on the serotype was reported in 68% of cases (16,191) in 2017 with serotypes 8, 3, 22F, 19A, 12F, 9N, 15A, 10A, 11A and 23B more frequently found and which were responsible for 66 % of all identified cases. [6]

The mortality of serious Pneumococcal infections can reach 20%, with a wide variability that depends mainly on the age of the patient (it rises as age increases) and comorbidity (it increases if the person also has other illnesses). Pneumococcal pneumonia is particularly threatening for the elderly population, where mortality can reach 30-40%, despite treatment with antibiotics and intensive care. As for meningitis, this can cause permanent disability and in the most serious cases lead to death; mortality reaches 40% in adults while it is around 1-3% in children under two years of age.

Despite its severity, pneumococcal infection can be prevented by vaccination. The inclusion of the vaccine in the vaccination schedule of children under the age of two has led to, in the United States, a reduction of almost 80% of cases of severe infection caused by the types of Pneumococcus present in the vaccine, and more generally, a halving of serious infections from all types of Pneumococcus. A significant reduction in infections (up to 40%) has also been demonstrated in the young adult population who have not undergone vaccination, especially family members of vaccinated children who have benefited from the effect of vaccination. The positive effect of vaccination was also recorded in European studies; despite the heterogeneity of the programmes and methods of data collection among the different countries, the reduction in cases of severe infection was around 40%, reaching the maximum benefit in children under two years of age. [7]

In 2017, as in previous years, serotypes 8, 3, 12F and 22F were the most frequent among the strains typed. Of these four serotypes, only 3 is present in the composition of the 13-valent conjugate vaccine (PCV13) while all are present in the polysaccharide 23-valent vaccine (PPSV23). On analysis of the serotypes identified in children between the ages of 0 and 4, the predominance of non-vaccine serotypes (those not contained in PCV13 and PCV10) is highlighted as an effect of the high vaccination coverage achieved in many regions. Among the vaccine serotypes still causing invasive disease in 2017, serotypes 3, 14 and 19F are to be noted. Among the non-vaccine serotypes on the rise in this age group are noted, in particular, 8, 10A, 12F, 15B and 23B. [5]

This serotype shift phenomenon must be accompanied by careful monitoring of the serotypes in circulation, improving in particular the identification of the pathogen in reported cases and planning new vaccination strategies by investing in the search for new vaccines. This evidence, however, must not be misleading regarding the direct benefit arising from the introduction of the vaccine, which significantly reduced the number of disease cases both in children and over 65s, as evidenced by the CDS surveillance data [7]

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