Among the causes of hospitalization of children in the United States, pneumonia is a leader. Streptococcus pneumoniae is the most common causative agent (17-28% of cases) of bacterial pneumonia and pleural empyema. This formidable complication represents 3% of all hospitalizations for pneumonia and a third for pneumococcal pneumonia.

According to data published in the January 2010 issue of Pediatrics, the widespread use in the United States of the 7-valent pneumococcal conjugate vaccine (PCV7), which successfully protects children from infections caused by Streptococcus pneumoniae, leads to an increase in the number of hospitalizations for empyema.

Despite the availability of clear evidence of a decrease in the incidence of invasive pneumococcal PCV7 infections, the effect of vaccination on the incidence of empyema has not been fully elucidated. Studies after the introduction of the vaccine into widespread clinical practice in the United States have shown conflicting results: the incidence of empyema has increased by 88% in Utah and 400% in California, while in Texas, this indicator decreased by 55% and in Quebec (Canada) remained generally the same.

The purpose of an epidemiological study conducted in the United States was to determine to what extent the percentage of hospitalizations for empyema in children in the United States has changed since the introduction of the pneumococcal conjugate vaccine.

Researchers determined the total number of hospital admissions for pleural empyema in 1997, 2000, 2003 and 2006. among children under the age of 18, using the national database of representative hospitalized children. Based on the US census, the values were converted to annual hospitalization rates per 100,000 children, which were then compared to each other.

In 2006, the total number of hospitalizations in children under 18 in the United States for pleural empyema was 2,898 (95% confidence interval 2532-3264), the hospitalization rate was 3.7 for 100,000 children (95% CI 3.3-4.4, 2), which is 70% higher than the same indicator in 1997, i.e. 2.2 per 100,000 children (95% CI 1.9-2, 5). The incidence of pneumonia, complicated by the development of empyema, pleural effusion, requiring pulmonary drainage or decortication (pleurectomy), also increased by 44%, or 5.5 per 100,000 children (CI 95% 4.8-6.1).

The incidence of invasive pneumococcal infections (pneumonia, sepsis or meningitis caused by Streptococcus pneumoniae) has decreased by 50% to 6.3 per 100,000 children (95% CI 5.7-6 , 9). The incidence of bacterial pneumonia decreased by 13% to 244.3 per 100,000 children (95% CI 231.1-257.5).

For example, in patients under 18, hospitalizations for empyema increased by almost 70% between 1997 and 2006, despite a drop in the incidence rate of invasive pneumococcal infections and bacterial pneumonia.

According to the study authors, the results can be explained by the absence of certain pneumococcal serotypes in the vaccine. Thus, the composition of the 7-valent pneumococcal conjugate vaccine includes serotypes 4, 6B, 9V, 14, 18C, 19F and 23F, but there is no serotype 1, which rarely causes bacterial pneumonia (4 -7% of cases), but is the main cause of pleural empyema (24-50%). In addition, the possibility of an increase in the proportion of pleural empyema is not excluded due to an increase in the prevalence of strains resistant to methicillin S. aureus.

Despite the results of the study, the authors do not encourage refusing vaccination against pneumococcal infection. On the contrary, the proportion of pneumonia tending to develop into a pleural empyema remains low, the advantages of vaccination are therefore obvious. Currently, a 10-valent pneumococcal conjugate vaccine is already registered in EU countries and 13-valent clinical trials are underway, which also contain serotypes 1, 5, 7F and 1, 3, 5, 6A, 7F, 19A, respectively. In the future, a number of additional studies are planned, which the authors say will show a significant decrease in hospitalizations for pleural empyema after the widespread introduction of new vaccines into clinical practice.