Coxiella burnetiiseroprevalence in unvaccinated veterinary workers in Australia: Evidence to support Q fever vaccination

Abstract

Q fever (caused by Coxiella burnetii) is a serious zoonotic disease that occurs almost worldwide. Occupational contact with animals increases the risk of exposure, and Q fever vaccination is recommended for veterinary workers in Australia. This study aimed to investigate C. burnetii seroprevalence among unvaccinated veterinary workers in Australia and determine factors associated with a positive serological result. During 2014 and 2015, convenience sampling at veterinary conferences and workplace vaccination clinics was undertaken. Participants completed a questionnaire and provided a blood sample for C. burnetii serology. Participants were predominantly veterinarians (77%), but veterinary support staff, animal scientists, and administration workers also participated. Blood samples (n = 192) were analysed by an immunofluorescence assay and considered positive where the phase I or phase II IgG titre was ≥1/50. Seroprevalence was 19% (36/192; 95% CI 14%–25%). A positive serological result was significantly associated with (a) working in outer regional/remote areas (odds ratio [OR] 6.2; 95% CI 1.9–20.8; reference = major cities; p = .009) and (b) having spent more than 50% of total career working with ruminants (OR 4.8; 95% CI 1.7–13.5; reference = <15% of career; p = .025). These findings confirm an increased risk of exposure to C. burnetii compared to the general population, providing new evidence to support Q fever vaccination of veterinary workers in Australia.

Coxiella burnetii seroprevalence and Q fever in Australian wildlife rehabilitators

“…Overall, three (2%) out of the 147 unvaccinated AWRs in this cohort self-reported having been medically diagnosed with QFD. This finding is similar to what was found in a study on Australian veterinary workers by Sellens et al [ 58 ], where 2% (4/192) of the cohort reported having QFD, but lower in comparison to another study of Australian cat breeders in which 6% (7/123) of the study population reported having had medically diagnosed QFD [ 62 ]. In all three studies, the level of QFD is substantially higher than the Australian annual notification rate of 0.002% [ 48 ].…”

“…This enabled a detailed analysis of the respective data sets to identify potential risk factors associated with seropositivity and having received Q fever vaccination. The 6.1% seroprevalence observed in the current study is lower than the 19% C. burnetii seroprevalence reported for a cohort of unvaccinated Australian veterinary workers, where increasing exposure to ruminants was identified as a significant risk factor for seropositivity [ 58 ]. International studies of livestock veterinarians have reported seroprevalence for C. burnetii as high as 65.1% [ 67 ].…”

“…The current study utilised IFA to confirm C. burnetii exposure by measuring levels of circulating C. burnetii antibody at a ‘point in time’. Although IFA is considered the ‘gold standard’ for human Q fever diagnosis [ 46 ], due to temporal decline in antibody levels and the variability in immune responses between individuals [ 58 ], the 6.1% seroprevalence observed in this study likely represents the minimum level of C. burnetii exposure amongst this cohort. This heterogeneity in antibody titres is demonstrated by the finding that only 30.7% (4/13) of vaccinated participants and two of the three participants with medically diagnosed QFD were seropositive at the time of blood collection ( Table 2 ).…”

“…The sample size for this study was calculated using Statulator software [ 20 ]. Assuming a nationwide average of 3% seroprevalence of Immunoglobulin G (IgG) antibodies to C. burnetii [ 30 ], an expected response rate of 15% [based on a serosurvey of veterinary workers [ 58 ]] and a national wildlife rehabilitator population size of 14,358, this study would require a sample size of 117 AWRs for estimating C. burnetii seroprevalence with 8% absolute precision and 95% confidence.…”

Subunit Vaccines Using TLR Triagonist Combination Adjuvants Provide Protection Against Coxiella burnetii While Minimizing Reactogenic Responses

“…These reactions necessitate costly pre-vaccination serologic screening and intradermal skin testing which delays vaccination (7)(8)(9). Surveys for anti-C. burnetii antibodies in at-risk populations, particularly those who work in animal husbandry and veterinary fields, reported seroprevalence rates of 18.3-45.13% (10)(11)(12). The high seroprevalence rates show that these groups that would most benefit from vaccination also bear the greatest risk of hyper-reactive responses.…”