Sequence based typing and pre-absorption test in retrospective analysis of a pseudo-outbreak of [i]Legionella[/i] infections differentiates true cases of legionellosis

National Institute of Public Health-National Institute of Hygiene, Warsaw, Poland
Department of Immunology and Clinical Allergology, Military Institute of Medicine, Warsaw, Poland
Serum Production, SSI Diagnostica, Statens Serum Institute, Hillerod, Denmark
Ann Agric Environ Med 2012;19(3):437–443
The aim of this study was elimination of false positive results obtained by the Chlamylege kit. Two serological kits (IgM ELISA [i]L.pneumophila[/i] sgs1-7; ImmuView[sup]TM[/sup] [i]L.pneumophila[/i] sg1/sg3) and pre-absorption tests (with [i]L.pneumophila[/i] sg1 and sg3 reference strains antigens) were used. 153 sera (79 patients) were examined. The high correlations were found between the results by both tests. Positive results by ELISA (sgs1-7) were found in 19/79 patients; by ImmuView[sup]TM[/sup] (sg1+sg3) in 16/63. In 8 patients, the dynamics of the IgM in pairs of sera was high (ratio ≥2). In 5/8 of those patients seroconversion was determined. Selected pre-absorbed sera (15 pairs) were tested simultaneously by the same tests. In 8/15 pairs of sera, the reduction of IgM levels in pre-absorbed sera was higher than 10. The reduction of IgM differed in sg1 and sg3 tests. The probability of infections due to [i]L.pneumophila[/i] sg3 (7 patients) and [i]L.pneumophila[/i] sg1 (5 patients) was based on the results of pre-absorption tests. The correlation between ELISA and ImmuView[sup]TM[/sup] tests of pre-absorbed sera was statistically significant (Po=0.0389). Moreover, genotyping of [i]L.pneumophila[/i] (SBT) directly in the sera of selected 15 patients (high IgM reduction) was carried out. Completed 7 alleles profile (ST36) was determined in one patient. However, a second patient had the same profile of 5 alleles, and similar reactions in pre-absorption tests. At least 4 sources of infections were suggested on the base of genotyping and pre-absorption results. Conclusions: Positive results obtained by molecular techniques (eg.PCR) in the diagnosis of [i]Legionella[/i] infections should be supplemented by other tests for confirmation of legionellosis. The sequence based typing carried out directly in clinical specimens seems to be a promising method.
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