Optimal assessment of the ability of children with recurrent respiratory tract infections to produce anti-polysaccharide antibodies.

Specific anti-polysaccharide antibody deficiency (SPAD) is an immune disorder. Diagnostic criteria have not yet been defined clearly. One hundred and seventy-six children evaluated for recurrent respiratory tract infections were analysed retrospectively. For each subject, specific anti-pneumococcal antibodies had been measured with two enzyme-linked immunosorbent assays (ELISAs), one overall assay (OA) using the 23-valent pneumococcal polysaccharide vaccine (23-PPSV) as detecting antigen and the other purified pneumococcal polysaccharide serotypes (serotype-specific assay, SSA) (serotypes 14, 19F and 23F). Antibody levels were measured before (n = 176) and after (n = 93) immunization with the 23-PPSV. Before immunization, low titres were found for 138 of 176 patients (78%) with OA, compared to 20 of 176 patients (11%) with the SSA. We found a significant correlation between OA and SSA results. After immunization, 88% (71 of 81) of the patients considered as responders in the OA test were also responders in the SSA; 93% (71 of 76) of the patients classified as responders according to the SSA were also responders in the OA. SPAD was diagnosed in 8% (seven of 93) of patients on the basis of the absence of response in both tests. Thus, we propose to use OA as a screening test for SPAD before 23-PPSV immunization. After immunization, SSA should be used only in case of a low response in OA. Only the absence of or a very low antibody response detected by both tests should be used as a diagnostic criterion for SPAD.

Evaluation of a WHO-Validated Serotype-Specific Serological Assay for the Diagnosis of Pneumococcal Etiology in Children with Community-Acquired Pneumonia.

BACKGROUND: The etiologic diagnosis of community-acquired pneumonia (CAP) remains challenging in children because blood cultures have low sensitivity. Novel approaches are needed to confirm the role of Streptococcus pneumoniae. METHODS: In this study, pneumococcal aetiology was determined by serology using a subset of blood samples collected during a prospective multicentre observational study of children <15 years of age hospitalised in Belgium with X-ray-confirmed CAP. Blood samples were collected at admission and 3-4 weeks later. Pneumococcal (P)-CAP was defined in the presence of a positive blood or pleural fluid culture. Serotyping of Streptococcus pneumoniae isolates was done with the Quellung reaction. Serological diagnosis was assessed for nine serotypes using World Health Organization validated IgG and IgA serotype-specific enzyme-linked immunosorbent assays (ELISAs). RESULTS: Paired admission/convalescent sera from 163 children were evaluated by ELISA (35 with proven P-CAP and 128 with non proven P-CAP). ELISA detected pneumococci in 82.8% of patients with proven P-CAP. The serotypes identified were the same as with the Quellung reaction in 82% and 59% of cases by IgG ELISA and IgA ELISA, respectively. Overall, ELISA identified a pneumococcal aetiology in 55% of patients with non-proven P-CAP. Serotypes 1 (51.6%), 7F (19%), and 5 (15.7%) were the most frequent according to IgG ELISA. CONCLUSIONS: In conclusion, the serological assay allows recognition of pneumococcal origin in 55% of CAP patients with negative culture. This assay should improve the diagnosis of P-CAP in children and could be a useful tool for future epidemiological studies on childhood CAP etiology.

Long- incubation time- interferon-gamma release assays in response to PPD-, ESAT-6- and/or CFP-10 for the diagnosis of Mycobacterium tuberculosis infection in children.

Background:Diagnosis of childhood active tuberculosis (aTB) or latent Mycobacterium tuberculosis (Mtb) infection (LTBI) remains a challenge, and replacement of tuberculin skin tests (TST) by commercialized interferon-gamma release assays (IGRA) is not currently recommended.Methods:266 children between 1 month and 15 years of age, 214 being at risk of recent Mtb infection and 51 being included as controls, were prospectively enrolled. According results of clinical evaluation, TST, chest X-Ray and microbiology, children were classified as non-infected, LTBI or aTB. Long-incubation time PPD-, ESAT-6-, and CFP-10-IGRA were performed and evaluated for their accuracy to correctly classify the children.Results:Whereas both TST and PPD-IGRA were suboptimal to detect aTB, combining CFP-10-IGRA with TST or with PPD-IGRA allowed us to detect all the children with aTB, with 96% specificity for children who were positive for CFP-10-IGRA. Moreover, combination of CFP-10- and PPD-IGRA also detected 96% of children classified as LTBI, but a strong IFN-γ response to CFP-10 (>500 pg/ml) was highly suggestive of aTB at least among children less than 3 years old.Conclusions:Long-incubation time CFP-10- and PPD-IGRA should help the clinicians to identify quickly aTB or LTBI in young children.

Humoral and B-cell memory responses in children five years after pertussis acellular vaccine priming.

The resurgence of pertussis suggests the need for greater efforts in understanding the long-lasting protective responses induced by vaccination. In this paper we dissect the persistence of humoral and B-cell memory responses induced by primary vaccination with two different acellular pertussis (aP) vaccines, hexavalent Hexavac(®) vaccine (Hexavac) (Sanofi Pasteur MSD) and Infanrix hexa(®) (Infanrix) (GlaxoSmithKline Biologicals). We evaluated the specific immune responses in the two groups of children, 5 years after primary vaccination by measuring the persistence of IgG and antibody secreting cells (ASC) specific for vaccine antigens. Part of the enrolled children received only primary vaccination, while others had the pre-school boost dose. A similar level of antigen-specific IgG and ASC was found in Infanrix and Hexavac vaccinated children. The mean IgG levels were significantly higher in children that received the pre-school boost as compared with children that did not receive the boost dose. A longer persistence after the pre-school boost of IgG-Pertussis Toxin (PT) and IgG-pertactin levels was observed in Infanrix primed children, but it was not statistically significant. More than 80% of children presented a positive ASC B memory response. Around 50% of children still presented protective IgG-PT levels which are reduced to 36% in no-boosted children. The pre-school booster dose restores the percentage of protected children above 50%. In conclusion our data underline the importance of giving a booster dose 5 years after primary vaccination and suggest the need for a new vaccine able to induce a long lasting protective response.