Routine vaccination of infants with the 7-valent pneumococcal conjugate vaccine (PCV7) began in 2000, but even before then, regional studies were showing that pneumonia-associated empyema was on the rise in children, the researchers say.
To get a sense of national trends, lead author Dr. Carlos G. Grijalva, from Vanderbilt University School of Medicine in Nashville, Tennessee, and colleagues retrieved data from the Nationwide Inpatient Sample – “the largest source of inpatient data publicly available in the United States” — for the years 1996-1999 and 2001-2007.
In the March 15 issue of Clinical Infectious Diseases, the researchers report that among children below 2 years of age, rates of pneumonia-associated empyema per 100,000 doubled over the study period, from 3.5 in 1996-1998 to 7.0 in 2005-2007, when there were 441 cases.
Among children 2-4 years old, rates nearly tripled, from 3.7 to 10.3 cases per 100,000. There were 1088 cases in 2007.
While rates of pneumococcal and streptococcal empyema remained stable in the younger age group, they rose by 2.17- and 2.80-fold in the older group.
Rates of staphylococcal empyema, however, rose by about 4-fold in both age groups (4.08-fold in the younger group and 3.76-fold in the older group).
Empyema classified as “other or unspecified” increased by a factor of 1.89 among infants < 2 and by a factor of 3.09 in the 2- to 4-year-olds.
The authors comment that in some years, cases of empyema were clustered in relatively few hospitals. In 2005, for example, 10% of hospitals reporting empyema in patients 2 to 4 years old accounted for half of the reported cases.
However, the investigators found that the early decreases in childhood pneumonia following the PCV7 introduction were sustained over the study period.
The initial reports of empyema in children in the U.S. were made prior to 2000, and similar increases have been reported in other countries, “suggesting that a direct association with the PCV7 vaccination program is unlikely.”
Dr. Grijalva’s group concludes, “The etiology of empyema is changing and…monitoring of empyema trends is warranted.”
Clin Infect Dis 2010.