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Volume 15, Number 10—October 2009

Dispatch

Immunologic Response of Unvaccinated Workers Exposed to Anthrax, Belgium

Pierre WattiauComments to Author , Marc Govaerts, Dimitrios Frangoulidis, David Fretin, Esther Kissling, Mieke Van Hessche, Bernard China, Martine Poncin, Yvo Pirenne, and Germaine Hanquet
Author affiliations: Veterinary and Agro-chemical Research Centre, Brussels, Belgium (P. Wattiau, M. Govaerts, D. Fretin, M. Van Hessche); Bundeswehr Institute of Microbiology, Munich, Germany (D. Frangoulidis); Institute of Public Health, Brussels, Belgium (E. Kissling, B. China, G. Hanquet); Occupational Medicine PROVIKMO, Verviers, Belgium (M. Poncin); Medical Inspection, Angleur, Belgium (Y. Pirenne); European Centre for Disease Control and Prevention, Stockholm, Sweden (E. Kissling)

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Table

Number of workers showing immunoreactivity against Bacillus anthracis antigens, as assayed by 3 different methods*

Status Anti-PA ELISA†
Western blot/dot blot‡
LT proliferation§
Year 1 Year 2 Year 1 Year 2 Ag = PA Ag = LF Ag = PA + LF Ag = conA
Negative 62 48 52 53 54 13
Positive 3 2 4 6 1¶# 0 41
Borderline 1 4 0 0 0 0

*PA, protective antigen; LT, lymphocyte; Ag, antigen; LF, lethal factor; conA, concanavalin A.
†Performed on serum samples according to the manufacturer’s instructions and thresholds (Serion, Würzburg, Germany). Note: 1 worker who tested positive at year 1 was not enrolled at year 2, and 3 workers tested negative at year 1 seroconverted to borderline at year 2.
‡Conducted only on serum samples found positive or borderline by anti-PA ELISA together with negative controls (n = 25). Dot blots were spotted with 1,000, 100, 10, and 1 ng of each purified PA and LF Ag purchased from Quadratech Ltd. (Epson, UK). Western blot antigens consisted in supernatant proteins derived from the culture of a reference B. anthracis strain.
§Assayed on blood samples from year 2 as described earlier (9) by using a proliferative index threshold set to 3× the index of a negative control stimulant (phosphate buffer). Stimulating Ag was used at a final concentration of 4 mg/mL (PA, LF, conA). ConA was used as positive control stimulant and was purchased from Sigma (St. Louis, MO, USA). Lymphocyte cultures found activatable by PA were confirmed by quantifying IFN-γ release by ELISA, according to the manufacturer’s instructions (Pierce, Rockford, IL, USA).
¶Serum samples from these workers tested positive by both Western blot and dot blot analysis.
#This culture was also stimulated by PA.

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