Assessment of IgA anti-PT and IgG anti-ACT reflex testing to improve Bordetella pertussis serodiagnosis in recently vaccinated subjects.

OBJECTIVES: Quantifying IgG antibodies to pertussis toxin (PT) is the most specific and sensitive method for the serodiagnosis of a Bordetella pertussis infection. Since PT is a component of acellular pertussis vaccines, anti-PT IgG is also induced by vaccination, precluding pertussis serodiagnosis based exclusively on anti-PT IgG in recently vaccinated subjects. Here, we aim to identify additional B. pertussis-specific serological markers that can discriminate between infection and recent vaccination. METHODS: The clinical usefulness of measuring IgA directed to the vaccine antigen PT and IgG directed to non-vaccine antigens (Fim2/3, LPS, ACT, CatACT) was evaluated in nine well characterized subject groups, aged 10-89 years (n = 390). Serum anti-PT IgG levels (>125 IU/mL) served as an indicator for a recent B. pertussis infection. Comparing symptomatic pertussis-infected subjects (n = 140) with recently vaccinated, non-infected subjects (n = 100) revealed the optimal cut-off, accuracy, sensitivity and specificity for each single parameter. RESULTS: For pertussis diagnosis in recently vaccinated subjects, the measurement of anti-PT IgA (cut-off 15 IU/mL) and anti-ACT IgG (cut-off 15 U/mL) resulted in accuracies of 95% (91.5-97.1) and 87.5% (82.7-91.1), sensitivities of 92.9% (87.4-96.0) and 83.6% (76.5-88.8) and specificities of 98% (93.0-99.4) and 93% (86.3-96.6), respectively. Comparing anti-PT IgA levels between the youngest (10-19 years, n = 38) and oldest (70-89 years, n = 17) age groups revealed an age-dependent increase in antibody levels in pertussis-infected subjects (p < 0.0001). CONCLUSIONS: Reflex testing of anti-PT IgA and anti-ACT IgG improves pertussis serodiagnosis in recently vaccinated symptomatic subjects with elevated anti-PT IgG levels. Furthermore, both markers can discriminate between vaccination and recent infection in pertussis serosurveillance studies.

Sera from different age cohorts in Belgium show limited cross-neutralization between the mumps vaccine and outbreak strains.

OBJECTIVES: Mumps used to affect children between 2 and 15 years old. The mumps-measles-rubella (MMR) vaccine is available, with vaccine coverage rate of about 85% after two vaccine doses. Recently new mumps outbreaks have emerged in highly vaccinated populations; the causes for these new outbreaks are yet unknown. We tested if a difference in seroneutralizing capacity against the vaccine and wild-type viruses existed and if waning immunity could be detected. METHODS: In this study, 570 serum samples (age group 2-3 years (n = 96), 8-9 years (n = 95), 13-14 years (n = 94), 18-20 years (n = 96), 24-26 years (n = 92) and 50 + years (n = 97)) in Belgium were tested in the rapid fluorescent foci inhibition test for their neutralizing capacity against the vaccine and wild-type viruses. RESULTS: Neutralizing antibodies against the vaccine strain were present in 84% (81/97) of the 2-3-year, 74% (70/95) of the 8-9-year, 81% (76/94) of the 13-14-year, 76% (73/96) of the 18-20-year, 67% (62/92) of the 24-26-year and 77% (75/97) of the 50+-year age group serum samples. For all age groups, only about half of these serum samples were also positive for the wild-type virus. The geometric mean titres for the vaccine and wild-type virus for all younger age groups, except for 24-26 years, were significantly different, demonstrating poor in vitro cross-neutralization. CONCLUSIONS: A possible contribution of antigenic differences between the genotype A and G mumps virus as well as other immune factors, in addition to lower-than-optimal vaccination coverage and waning immunity, could explain the poor in vitro cross-neutralization and should be further studied.

Community transmission of influenza A (H1N1)v virus at a rock festival in Belgium, 2-5 July 2009.

On 6 July 2009 the Belgian enhanced surveillance system for influenza-like illness among travellers returning from influenza A(H1N1)v affected areas detected a case linked to a rock festival which took place on 2-5 July. The health authorities implemented communication and control measures leading to the detection of additional cases. This paper describes the outbreak and its impact on the management of the influenza pandemic in Belgium.

Pediatric human immunodeficiency virus screening in an African district hospital.

In order to evaluate alternative tests and strategies to simplify pediatric human immunodeficiency virus (HIV) screening at the district hospital level, a cross-sectional exploratory study was organized in the Democratic Republic of the Congo. Venous and capillary phlebotomies were performed on 941 Congolese children, aged 1 month to 12 years (153 children under 18 months and 788 children more than 18 months old). The HIV prevalence rate was 4.7%. An algorithm for children more than 18 months old, using serial rapid tests (Determine, InstantScreen, and Uni-Gold) performed on capillary blood stored in EDTA tubes, had a sensitivity of 100.0% (95% confidence interval [CI], 88.9 to 100.0%) and a specificity of 100.0% (95% CI, 99.5 to 100.0%). The results of this study suggest that the ultrasensitive p24 antigen assay may be performed on capillary plasma stored on filter paper (sensitivity and specificity, 100.0%; n=87) instead of venous plasma (sensitivity, 92.3%; specificity, 100.0%; n=150). The use of glucolets (instruments used to perform capillary phlebotomies), instead of syringes and needles, may reduce procedural pain and the risk of needle stick injuries at a comparable cost. Compared to the reference, HIV could have been correctly excluded based on one rapid test for at least 90% of these children. The results of this study point towards underutilized opportunities to simplify phlebotomy and pediatric HIV screening.