Limits...
Characterization of the extent of a large outbreak of Legionnaires' disease by serological assays.

Simonsen Ø, Wedege E, Kanestrøm A, Bolstad K, Aaberge IS, Ragnhildstveit E, Ringstad J - BMC Infect. Dis. (2015)

Bottom Line: About the same proportion (70%) of the urinary antigen positive and negative LD cases had antibodies to the serogroup-specific lipopolysaccharide of the outbreak strain.The acute-phase tests (culture, polymerase chain reaction, and urinary antigen) identified less than 55% of the 103 patients in this outbreak.Serological testing thus remains an important supplement for diagnosis of LD and for determination of outbreak cases.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Østfold Hospital Trust, Fredrikstad, Norway. oystein.simonsen@so-hf.no.

ABSTRACT

Background: In May 2005, a long-distance outbreak of Legionnaires' disease (LD) caused by Legionella pneumophila serogroup 1 occurred in south-east Norway. The initial outbreak investigation without serology identified 56 laboratory-confirmed LD cases of whom 10 died. However, 116 patients with community-acquired pneumonia might belong to the outbreak based on epidemiological investigations, but acute laboratory tests other than serology were negative or not performed. To assess the true extent of the outbreak, we evaluated two serological assays in order to reclassify the 116 patients with indeterminate case status.

Methods: Two polyvalent antibody tests, a serogroup 1-6 immunofluorescence assay (IFA) and a serogroup 1-7 enzyme-linked immunosorbent assay (ELISA) were used. They were evaluated with cases defined as culture- or urinary antigen positive LD patients (n=40) and non-cases defined as confirmed non-LD patients (n=39) and healthy control subjects (n=62). The 116 patients, who were negative in culture, polymerase chain reaction and/or urinary antigen tests, were analysed by the same serological assays. Antibodies to the outbreak strain were determined by immunoblotting.

Results: In the evaluation study, the sensitivity and specificity of a ≥4-fold IFA titre change was 38% and 100%, respectively, with corresponding values of 30% and 99% for seroconversion in ELISA. A single high positive IFA titre yielded sensitivity and specificity of 73% and 97%, respectively, with corresponding values of 68% and 96% for a single high immunoglobulin (Ig) G and/or IgM in ELISA. Based on this evaluation, the following serological testing identified 47 more LD cases, and the outbreak thus comprised 103 cases with a case fatality rate of 10%. About the same proportion (70%) of the urinary antigen positive and negative LD cases had antibodies to the serogroup-specific lipopolysaccharide of the outbreak strain. In addition to the 103 LD cases, Legionella infection could not be verified or excluded in 32 patients based on epidemiology and/or lack of microbiological sampling.

Conclusions: The acute-phase tests (culture, polymerase chain reaction, and urinary antigen) identified less than 55% of the 103 patients in this outbreak. Serological testing thus remains an important supplement for diagnosis of LD and for determination of outbreak cases.

No MeSH data available.


Related in: MedlinePlus

Cases of Legionnaires’ disease and community-acquired pneumonia (CAP) by date of admission to the hospital.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4383209&req=5

Fig2: Cases of Legionnaires’ disease and community-acquired pneumonia (CAP) by date of admission to the hospital.

Mentions: Compared with all 94 non-LD patients (56 patients with confirmed non-LD and 38 patients with negative serology, Figure 1), LD cases had more severe pneumonia (P = 0.048) and a higher proportion of ICU admission (P = 0.019) than non-LD patients (Table 4). However, chronic respiratory disease was more frequent in the non-LD group (P = 0.002). The group of 32 CAP patients with uncertain Legionella status had a high mean age and mortality, but statistical comparisons of this group with the two others are less reliable due to its heterogeneity as described above. Figure 2 demonstrates the hospitalisation date for patients with LD diagnosed by culture/PCR/UAT and serology, respectively, non-LD, and CAP of unknown aetiology during the defined five-week period. The number of admissions for LD cases mirrored the outbreak epidemic curve [16]. The non-LD admission curve, which was expected to fluctuate around a mean of 2.3 per day based on hospitalization rates in 2001 – 2004, also peaked, but two days after the outbreak alert. This curve indicated an over-referral of approximately 15 non-LD patients probably caused by the media attention following the outbreak. The 32 patients with CAP of unknown aetiology were scattered throughout the period with a peak two days before the outbreak alert.Table 4


Characterization of the extent of a large outbreak of Legionnaires' disease by serological assays.

Simonsen Ø, Wedege E, Kanestrøm A, Bolstad K, Aaberge IS, Ragnhildstveit E, Ringstad J - BMC Infect. Dis. (2015)

Cases of Legionnaires’ disease and community-acquired pneumonia (CAP) by date of admission to the hospital.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4383209&req=5

Fig2: Cases of Legionnaires’ disease and community-acquired pneumonia (CAP) by date of admission to the hospital.
Mentions: Compared with all 94 non-LD patients (56 patients with confirmed non-LD and 38 patients with negative serology, Figure 1), LD cases had more severe pneumonia (P = 0.048) and a higher proportion of ICU admission (P = 0.019) than non-LD patients (Table 4). However, chronic respiratory disease was more frequent in the non-LD group (P = 0.002). The group of 32 CAP patients with uncertain Legionella status had a high mean age and mortality, but statistical comparisons of this group with the two others are less reliable due to its heterogeneity as described above. Figure 2 demonstrates the hospitalisation date for patients with LD diagnosed by culture/PCR/UAT and serology, respectively, non-LD, and CAP of unknown aetiology during the defined five-week period. The number of admissions for LD cases mirrored the outbreak epidemic curve [16]. The non-LD admission curve, which was expected to fluctuate around a mean of 2.3 per day based on hospitalization rates in 2001 – 2004, also peaked, but two days after the outbreak alert. This curve indicated an over-referral of approximately 15 non-LD patients probably caused by the media attention following the outbreak. The 32 patients with CAP of unknown aetiology were scattered throughout the period with a peak two days before the outbreak alert.Table 4

Bottom Line: About the same proportion (70%) of the urinary antigen positive and negative LD cases had antibodies to the serogroup-specific lipopolysaccharide of the outbreak strain.The acute-phase tests (culture, polymerase chain reaction, and urinary antigen) identified less than 55% of the 103 patients in this outbreak.Serological testing thus remains an important supplement for diagnosis of LD and for determination of outbreak cases.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Østfold Hospital Trust, Fredrikstad, Norway. oystein.simonsen@so-hf.no.

ABSTRACT

Background: In May 2005, a long-distance outbreak of Legionnaires' disease (LD) caused by Legionella pneumophila serogroup 1 occurred in south-east Norway. The initial outbreak investigation without serology identified 56 laboratory-confirmed LD cases of whom 10 died. However, 116 patients with community-acquired pneumonia might belong to the outbreak based on epidemiological investigations, but acute laboratory tests other than serology were negative or not performed. To assess the true extent of the outbreak, we evaluated two serological assays in order to reclassify the 116 patients with indeterminate case status.

Methods: Two polyvalent antibody tests, a serogroup 1-6 immunofluorescence assay (IFA) and a serogroup 1-7 enzyme-linked immunosorbent assay (ELISA) were used. They were evaluated with cases defined as culture- or urinary antigen positive LD patients (n=40) and non-cases defined as confirmed non-LD patients (n=39) and healthy control subjects (n=62). The 116 patients, who were negative in culture, polymerase chain reaction and/or urinary antigen tests, were analysed by the same serological assays. Antibodies to the outbreak strain were determined by immunoblotting.

Results: In the evaluation study, the sensitivity and specificity of a ≥4-fold IFA titre change was 38% and 100%, respectively, with corresponding values of 30% and 99% for seroconversion in ELISA. A single high positive IFA titre yielded sensitivity and specificity of 73% and 97%, respectively, with corresponding values of 68% and 96% for a single high immunoglobulin (Ig) G and/or IgM in ELISA. Based on this evaluation, the following serological testing identified 47 more LD cases, and the outbreak thus comprised 103 cases with a case fatality rate of 10%. About the same proportion (70%) of the urinary antigen positive and negative LD cases had antibodies to the serogroup-specific lipopolysaccharide of the outbreak strain. In addition to the 103 LD cases, Legionella infection could not be verified or excluded in 32 patients based on epidemiology and/or lack of microbiological sampling.

Conclusions: The acute-phase tests (culture, polymerase chain reaction, and urinary antigen) identified less than 55% of the 103 patients in this outbreak. Serological testing thus remains an important supplement for diagnosis of LD and for determination of outbreak cases.

No MeSH data available.


Related in: MedlinePlus