An active surveillance system of invasive pneumococcal disease (IPD) started on September 2008 in Lombardy, Italy, among children aged less than 60 months and admitted for suspicion of IPD at emergency room of ten hospitals. This study examined the clinical characteristics of children enrolled up to December 2010, that is just before the introduction in this region of voluntary mass vaccination, free of charge, based on the 13-valent pneumococcal conjugate vaccine (PCV13). Two hundred fifty one children were suspected and 20 were confirmed as having IPD, based on isolation of Streptococcus pneumoniae from blood. Thirty-nine percent of children had received pneumococcal vaccination previously, and full vaccination with three doses of hepta-valent vaccine (PCV7) had been administered in 21.4%. Co-morbidity conditions were more frequent in children with confirmed than non-confirmed IPD (10.0% vs. 0.9%). The annual incidence rate of confirmed IPD was 28.6/100,000 (binomial 95% confidence interval, 18.6 to 44.1/100,000. Among confirmed IPD children, 11 exhibited pneumonia with bacteremia, 6 bacteremia without focus, 2 septicemia, 1 meningitis. Seventeen (85%) isolates were identified, and nine serotypes. The overall serotype coverage was 29.4% for PCV7 and 82.3% for PCV13. In non-vaccinated children, the coverage of PCV7 and PCV13 was 41.7% and 75.0%, respectively. Non-vaccine serotypes 12B, 15C, and 23B were identified. Antibiotic resistance was found in seven children, that is against penicillin (serotype 15C), erythromycin (14, 19A, 19F), tetracycline (15C, 19F), chloramphenicol (23F), and trimethoprim-sulfamethoxazole (23F). Two of these children had received antibiotic therapy (penicillin or azithromycin) during the week before hospital admission. The coverage vaccination rate in Lombardy was relatively low during the surveillance period and serotype distribution widespread. The introduction of PCV13 and a mass vaccination program in young children might impact positively on invasive pneumococcal disease in this surveilled population. Active long-term surveillance of non-vaccine serotypes is required wordwide.
Streptococcus pneumoniae (S. pneumoniae) is a leading cause of invasive infection and vaccine-preventable deaths among young children [1-4]. Decline in invasive pneumococcal disease (IPD) has been observed in countries which introduced the heptavalent pneumococcal conjugate vaccine (PCV7) in their immunization programs [5-6], with higher reduction in the US, where also decline in IPD mortality occurred [
In Italy, few local studies have been conducted in the past in children aged less than 60 months [11-15]. Recently Azzari et al. [
Indeed, while Lombardy is a crucial region with around 10,000,000 resident people in 2011, the characteristics of IPD in young children, including the pneumococcal serotype distribution, have been never actively investigated.
The main objective of this study was to describe the clinical characteristics of the invasive pneumococcal disease in young children residing in the North-West Lombardy, Italy, and to determine the serotype distribution of S. pneumoniae occurring just before the introduction of the PCV13, that was licensed in Italy for commercialization on April 30, 2010.
These data would provide general epidemiological information useful to better examine the traits of invasive pneumococcal disease in young children, and further to help the Health Authorities and industry for hopefully improving immunization strategies.
This study is a part of an active surveillance of IPD in young children that started on September 01, 2008, in North-West Lombardy, Italy, also including the municipality of Milan. Cases of suspected IPD were collected from ten hospitals homogeneously located in the area delimited by four Reference Local Health Authorities districts. This study analyzed children enrolled up to December 31, 2010, that is before of the introduction of a new regular vaccination strategy and implementation of the PCV13 in Lombardy. The scrutinized area comprised at the beginning of the surveillance around 3,500,000 people, including 130,000 children aged less than 60 months, of whom 30,000 (12,000 aged less than 24 months) referenced to the participant hospitals.
Children admitted at emergency room of the hospitals were assessed for eligibility. Inclusion criteria were: age at admission 28 days - 59 months; being residing in the monitored area; suspicion of IPD, that is any S. pneumoniae clinical syndrome; negative urinalysis for urinary tract infections based on fast urine test; C-reactive protein > 15 mg/L. The additional inclusion criterion and/or body (rectal) temperature ≥ 38˚C was considered in children aged ≤ 36 months, as it may be per se suggestive of IPD within this range of age [
The study was carried out in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. The ethics committee of each hospital approved the study protocol. Written informed consent was obtained from the parents or legal guardian after the study had been fully explained.
A case of confirmed IPD was defined in accordance with the Centers for Disease Control and Prevention (Atlanta, GA, USA) [19,20]. Definition of specific IPD syndrome was in accordance with the International Classification of Diseases-9 [
Blood samples were taken in children within 24 h of recruitment. Cerebrospinal fluid samples were additionally taken in children with clinical syndrome of sepsis and/or meningitis for confirmation. S. pneumoniae isolates were identified by standardized laboratory procedures. Fresh cultures of isolates on blood agar plates and in Amies medium swab were sent to the central reference laboratory (Milan, Italy) for analysis and stored on beads at –70˚C. Isolates were then confirmed for S. pneumoniae by testing for alpha haemolysis on blood agar, optochin susceptibility and bile solubility.
Serotyping was based on Omni serum (Statens Serum Institut, Copenhagen, Denmark) that includes antibodies to all recognized S. pneumoniae serotypes. A suspension of the test organism was prepared in saline solution 0.9% from well isolated colonies grown on sheep blood agar plates for 18 to 24 h in 5% CO2 at 35˚C. One drop of this suspension was mixed with 1 drop of antiserum and 1 drop of methylene blue and, after incubation at room temperature for 10 min, examined at 1000× magnification. Visible evidence of capsular swelling with Omni serum, i.e., a positive Quellung reaction, was considered positive, and followed by type specific antisera. Antimicrobial susceptibility against penicillin G, ceftriaxone, erythromycin, tetracycline, trimethoprim-sulfamethoxazole, chloramphenicol, levofloxacin, linezolid and vancomycin was performed by the E test method (AB Biodisk, Solana, Sweden) on Mueller-Hinton agar supplemented with 5% defibrinated sheep blood (bioMérieux Italia Spa, Bagno a Ripoli, Italy). The minimal inhibitory concentration was defined in accordance with the Clinical and Laboratory Standards Institute breakpoints [
Comparison between independent groups was performed by the Chi-square or Fisher’s exact test or Mann-Whitney U test, as appropriate. Significance was posed at P < 0.05 (two-tails). The statistical analyses were done using the SPSS software, version 17.0 for Windows (SPSS Inc.Chicago, IL).
Two hundred fifty one children (140 boys, 111 girls; mean age [SD] 27.5 [16.8] months) were recruited. Blood testing data were available in 236 cases, and 20 (13 boys, 7 girls) were confirmed as having IPD. All of them were hospitalized. No fatality outcome occurred during hospitalization. The pooled annual incidence rate of confirmed IPD was 28.6/100,000 (binomial 95% confidence interval, 18.6 to 44.1/100,000), that is 30.0/100,000 (16.0 to 46.9/100,000) in infants and 26.2/100,000 (14.8 to 48.9/100,000) in children aged 2 - 4 years.