Identification of an unusual cluster of human granulocytic anaplasmosis in the Estrie region, Québec, Canada in 2021

Abstract

Background Human granulocytic anaplasmosis (HGA) is a potentially severe tick-borne infection caused by the bacterium Anaplasma phagocytophilum ( A. phagocytophilum ) of the genus Rickettsia. Here, we describe the epidemiological and clinical characteristics of an unusual cluster of HGA cases detected in the Estrie region in Québec, Canada, during the 2021 transmission season. Methods Confirmed cases of HGA were defined as individuals with typical clinical manifestations and a positive polymerase chain reaction assay. The cases were interviewed using a structured questionnaire and clinical data was obtained from medical records. Results A total of 25 confirmed cases were identified during the 2021 transmission season, thus constituting the largest known cluster of HGA in Canada. The most common symptoms reported were fever, fatigue and headaches. Laboratory investigations found that 20 (80%) of the patients had thrombocytopenia and 18 (72%) had leukopenia at presentation. Almost half of the patients required hospitalization (n=11, 44%), with a median duration of four days (interquartile range [IQR] 2.5–5 days), including one patient who required intensive care. No deaths were recorded during the study. Epidemiological investigation found that all cases were domestically acquired, and yard maintenance was the most prevalent at-risk activity identified. Only seven (28%) cases had been aware of a tick bite in the previous two weeks. Conclusion Detection of this unusual cluster of HGA cases provides further evidence that A. phagocytophilum may now be established along the southern border of Québec. Clinicians should consider HGA when assessing patients with typical symptoms and recent exposure to high-risk environments for tick bite.

Case Series of Jamestown Canyon Virus Infections with Neurologic Outcomes, Canada, 2011–2016

“…It is possible that A . phagocytophilum seropositivity reflects either a previous infection or co-infection, because anaplasmosis is a known emerging infection in many regions within Canada, including Quebec ( 40 – 42 ).…”

The added value of One Health surveillance: data from questing ticks can provide an early signal for anaplasmosis outbreaks in animals and humans

“…In this article, we describe the changes over time in the prevalence of Ap infection in questing ticks in a region where an outbreak of AGA and HGA cases (Campeau et al, 2022) was recently identified. The findings show a significant increase in Ap prevalence between 2019 and 2021.…”

“…The increase in Ap prevalence in questing ticks is likely to be one of the drivers of the first outbreak of AGA and HGA cases in 2021. While Campeau et al (2022) highlight the need to include GA as a Canadian human reportable disease to support early identification of outbreaks, we aim to push this reflection further. We think that this article illustrates the importance of integrating environmental data (i.e., questing ticks) in TBD surveillance…”

“…The total number of animal cases remains unknown because AGA is not a reportable disease. Between May and November, 25 confirmed HGA cases, including 11 hospitalizations, were confirmed by Estrie Public Health Authority (Campeau et al, 2022). All AGA or HGA cases were residents of Estrie or reputed to have visited the region delimited by two local health service units named La Pommeraie and Haute-Yamaska.…”

“…All AGA or HGA cases were residents of Estrie or reputed to have visited the region delimited by two local health service units named La Pommeraie and Haute-Yamaska. The municipality of Bromont was mostly affected, with 64% of HGA confirmed cases (Campeau et al, 2022). Even though this region is known to have high LD incidence in humans, the sudden outbreak of human GA cases generated concerns in the population.…”