Enzyme-linked immunosorbent assays in seroprevalence studies of Q fever: the need for cut-off adaptation and the consequences for prevalence data

Evidence of exposure to C. burnetii among slaughterhouse workers in western Kenya

Q fever, caused by C. burnetii, has been reported in slaughterhouse workers worldwide. The most reported risk factor for seropositivity is the workers' role in the slaughterhouse. This study examined the seroprevalence and risk factors for antibodies to C. burnetii in slaughterhouse workers in western Kenya to fill a data gap relating to this emerging disease in East Africa.

Individuals were recruited from all consenting slaughterhouses in the study area between February and November 2012. Information was collected from participating workers regarding demographic data, animals slaughtered and role in the slaughterhouse. Sera samples were screened for antibodies to C. burnetii using a commercial ELISA and risk factors associated with seropositivity were identified using multi-level logistic regression analysis.

Slaughterhouse workers (n = 566) were recruited from 84 ruminant slaughterhouses in western Kenya. The seroprevalence of antibodies to C. burnetii was 37.1% (95% Confidence Interval (CI) 33.2–41.2%). The risk factors identified for C. burnetii seropositivity included: male workers compared to female workers, odds ratio (OR) 5.40 (95% CI 1.38–21.22); slaughtering cattle and small ruminants compared to those who only slaughtered cattle, OR 1.52 (95% CI 1.06–2.19). In addition, specific roles in the slaughterhouse were associated with increased odds of being seropositive, including cleaning the slaughterhouse, OR 3.98 (95% CI 1.39–11.43); cleaning the intestines, OR 3.24 (95% CI 1.36–7.73); and flaying the carcass OR 2.63 (95% CI 1.46–4.75) compared to being the slaughterman or foreman.

We identified that slaughterhouse workers have a higher seroprevalence of antibodies to C. burnetii compared to published values in the general population from the same area. Slaughterhouse workers therefore represent an occupational risk group in this East African setting. Workers with increased contact with the viscera and fluids are at higher risk for exposure to C. burnetii. Education of workers may reduce transmission, but an alternative approach may be to consider the benefits of vaccination in high-risk groups.

Incidence of chronic Q fever and chronic fatigue syndrome: A 6 year follow-up of a large Q fever outbreak

Acute Q fever is a generally self-limiting infection caused by the intracellular gram-negative bacterium Coxiella burnetii. For yet unknown reasons, a subset of patients develops chronic infection. Furthermore, chronic fatigue syndrome (CFS) as post-acute Q fever sequelae has been described. We here investigated the rates of chronic Q fever and incidences of CFS 6 years after one of the largest European Q fever outbreaks that occurred in Jena, Germany in 2005 with 331 reported cases, who lived in proximity of a grazing flock of sheep. A total of 80 patients and their 52 non-diseased household members from the former outbreak, were enrolled 6 years after the outbreak. Blood samples were collected and tested for chronic Q fever which was determined by seroprevalence using referenced immunofluorescence assays. Also, the presence of CFS was assessed using the Short Form Symptom Inventory developed by the Centers (United States) for Disease Control and Prevention (SF CDC- SI). In 80 out of 132 (60.6%) study participants, previous Q fever infection was confirmed serologically, while no previous infection was detected in the 52 household members. None of the participants fulfilled the serological criteria of chronic Q fever. The evaluation of the CDC-SI did not show any differences between the two groups. Also, there was no difference between both groups regarding fulfillment of CFS-defining criteria (n = 3 (3.8%; sero-positive) versus n = 2 (3.8%; sero-negative), p = 0.655). Our 6-year follow-up study of a large Q fever outbreak did not find evidence of chronic Q fever or post Q fever CFS. There was no asymptomatic sero-positivity in household members of Q fever patients.

A Freedom of Coxiella burnetii Infection Survey in European Bison (Bison bonasus) in Poland

Simple Summary

Q fever is one of the important diseases transmissible from animals to humans. The source of infection can be numerous species of animals including mammals, birds, reptiles, amphibians as well as ticks. The role of wildlife in its epidemiology is poorly understood. Therefore, we examined 523 sera samples obtained from European bison for the presence of specific antibodies to assess whether infection occurs in this species and whether European bison may be an important source of infection in the natural environment as suggested by historical reports. The antibodies were found only in one free-living bull, while two other samples were doubtful. The results suggest the transmission of infection to the European bison was rather accidental and its role as an important source of infection nowadays is unlikely.

Abstract

Q fever is an important zoonosis caused by the intracellular Gram-negative bacteria Coxiella burnetii. The source of infection are numerous species of mammals, birds, reptiles and amphibians, as well as ticks. The disease is widespread throughout Europe, but the role of wildlife in its epidemiology is poorly understood. The European bison (Bison bonasus) population has been growing European-wide quite dynamically over the last few years. The aim of this study was to determine whether C. burnetii infection occurs in European bison and whether it can be considered an important bacterial reservoir in the natural environment. Five hundred and twenty three samples of European bison sera originating from 14 (out of the 26 existing) Polish populations were examined for the presence of specific antibodies using an ID Screen Q Fever Indirect Multi-species ELISA test. Only one (0.19%) serum sample was positive in ELISA, and two other samples were doubtful. The only seropositive animal found in this study was a free-living bull. It suggests possible transmission from domestic cattle by sharing pastures. The transmission of C. burnetii into the European bison was rather accidental in the country and its role as an important wild reservoir is unlikely. Since no tests are available for wildlife ruminants there is a need for the adaptation of the available tests.

Prevalence of Coxiella burnetii seropositivity and shedding in farm, pet and feral cats and associated risk factors in farm cats in Quebec, Canada

Cats represent a potential source of Coxiella burnetii, the aetiological agent of Q fever in humans. The prevalence and risk factors of C. burnetii infection in farm, pet and feral cats were studied in Quebec, Canada, using a cross-sectional study. Serum samples were tested using a specific enzyme-linked immunosorbent assay (ELISA) for the presence of antibodies against C. burnetii, whereas rectal swabs were assayed using real-time quantitative polymerase chain reaction (qPCR) for the molecular detection of the bacteria. Potential risk factors for farm cats were investigated using clinical examinations, questionnaires and results from a concurrent study on C. burnetii farm status. A total of 184 cats were tested: 59 from ruminant farms, 73 pets and 52 feral cats. Among farm cats, 2/59 (3.4%) were ELISA-positive, 3/59 (5.1%) were ELISA-doubtful and 1/59 (1.7%) was qPCR-positive. All pets and feral cats were negative to C. burnetii ELISA and qPCR. Farm cat positivity was associated with a positive C. burnetii status on the ruminant farm (prevalence ratio = 7.6, P = 0.03). Our results suggest that although pet and feral cats do not seem to pose a great C. burnetii risk to public health, more active care should be taken when in contact with cats from ruminant farms.

Current approaches for the detection of Coxiella burnetii infection in humans and animals

Q fever (coxiellosis), caused by Coxiella burnetii, is an emerging or re-emerging zoonotic disease of public health significance and with worldwide distribution. As a causal agent of the one among the 13 global priority zoonoses, having the infectious dose as low as one bacterium, C. burnetii has been regarded as an obligate intracellular bacterial pathogen. The agent has been classified as a Group B bioterrorism agent by the Centre for Disease Control and Prevention (CDC), and the disease is included in the World Organisation for Animal Health (OIE) list of notifiable diseases. It is mainly transmitted through airborne route in humans and animals. Isolation of C. burnetii, using standard routine laboratory culture techniques was impossible until formulation of axenic-based medium. However, it is still to be included among routinely isolated laboratory pathogen, accounting prolonged incubation period (~7 days) and requirement of specific oxygen concentration (2.5% O₂). Therefore, indirect diagnostic tools have been mainly used for its diagnosis. So far serology has been mostly used for testing for C. burnetii infection. The detection of C. burnetii DNA by PCR in various clinical samples have also been widely used. The disease has remained largely under-reported, underdiagnosed and as a masked zoonosis; and therefore, needs to be explored through well-planned scientific studies for knowing its true status and likely it impact in humans and animals by employing state-of-the-art diagnostics, identifying its diverse and new host range, as well as risk factors involved in different geo-climatic, behavioural and social settings as well as risk groups. Here, we reviewed the current approaches used for the detection of C. burnetii infection in humans and animals at the population and individual level.

Who is at risk of occupational Q fever: new insights from a multi-profession cross-sectional study

OBJECTIVES

Q fever is a zoonosis caused by the bacterium Coxiella burnetii. It is recognised as an occupational hazard for individuals who are in regular contact with animal birth products. Data from the literature are not comparable because different serological assays perform very differently in detecting past infections. It is therefore essential to choose the right assay for obtaining reliable data of seroprevalence. Obstetricians are another profession potentially at risk of Q fever. They can be infected from birth products of women with Q fever during pregnancy. There is little data, however, for Q fever in this occupational group. Our study therefore had two purposes. The first was to obtain reliable seroprevalence data for occupational groups in regular contact with animal birth products by using an assay with proven excellent sensitivity and specificity for detecting past infections. The second purpose was to obtain primary data for obstetricians.

DESIGN

We carried out a cross-sectional study.

SETTING

The study included shepherds, cattle farmers, veterinarians and obstetricians from Thuringia.

PARTICIPANTS

77 shepherds, 74 veterinarians, 14 cattle farmers, 17 office employees and 68 obstetricians participated. The control group consisted of 92 blood donors.

PRIMARY OUTCOME MEASURE

The primary outcome measure was C. burnetii phase II specific IgG. The assay used was evaluated for this purpose in a previous study.

RESULTS

Of the 250 blood samples we analysed, the very highest seroprevalences (64%-77%) occurred in individuals with frequent animal contact. There were no significant differences between shepherds, cattle farmers and veterinarians. The seroprevalence in people working in administration was lower but still significantly greater than the control. No obstetricians or midwives tested positive.

CONCLUSIONS

Shepherds, cattle farmers and veterinarians have a high risk of C. burnetii infection. However, our study clearly proves that there was no increased risk for people working in an obstetric department.

Cost-effectiveness of Screening Program for Chronic Q Fever, the Netherlands

In the aftermath of a large Q fever (QF) epidemic in the Netherlands during 2007-2010, new chronic QF (CQF) patients continue to be detected. We developed a health-economic decision model to evaluate the cost-effectiveness of a 1-time screening program for CQF 7 years after the epidemic. The model was parameterized with spatial data on QF notifications for the Netherlands, prevalence data from targeted screening studies, and clinical data from the national QF database. The cost-effectiveness of screening varied substantially among subpopulations and geographic areas. Screening that focused on cardiovascular risk patients in areas with high QF incidence during the epidemic ranged from cost-saving to €31,373 per quality-adjusted life year gained, depending on the method to estimate the prevalence of CQF. The cost per quality-adjusted life year of mass screening of all older adults was €70,000 in the most optimistic scenario.