IN HUMANS
PREVALENCE AND RISK FACTORS • Q fever in humans is uncommonly reported (approximately 500 notified cases per year in Australia) but there is likely a reasonable degree of under-reporting due to asymptomatic infection and difficulty in diagnosis. This is supported by seroprevalence rates of up to 7% in the general population. 13 • There are regional differences in incidence across Australia, with New South Wales and Queensland accounting for 87% of total notifications. 14 Prevalence is highest in Queensland (6.3 cases annually per 100,000 population), followed by New South Wales (3.1 cases annually per 100,000 population) and South Australia (1.1 cases annually per 100,000 population). 15 Individuals living on farms in outer regional or remote areas are at greater risk of contracting Q fever. 13,16 • Gender and age differences are seen, with notifications more common in older males. 14 • Occupational exposure through the livestock industry (farmers, abattoir workers, shearers, livestock transport drivers, veterinarians, veterinary nurses etc.) or exposure to other animals, particularly parturient animals, is a risk factor for Q fever. 14,15 Almost two-thirds of notifications are from individuals with known occupational or environmental risk factors. 14 Coxiella burnetii is highly infectious and Q fever can occur in people with remote (e.g. living down-wind from abattoirs) or very transient exposure, hence clinical history and consideration of Q fever is very important in making a diagnosis. Human-to-human transmission is extremely rare. • Seroprevalence in (unvaccinated) veterinary workers in Australia was 19%, with seropositivity associated with working in an outer regional/remote area and having spent >50% of total career working with ruminants. 17 • Sporadic cases of disease in veterinary staff, animal carers, and breeders working with dogs and cats are reported. 3,18,19 CLINICAL DISEASE • Q fever can cause both acute and chronic infection, ranging in severity from asymptomatic to mild to severe. Differences in clinical manifestations are seen with geographic variation which may be the result of differences in regional strains of Coxiella burnetii . • Acutely, Q fever can manifest as an influenza-like illness with fever, headache, malaise and myalgia. Biochemical hepatitis (elevation in liver function tests without clinical evidence of hepatitis) is common and clinically evident hepatosplenomegaly may be present. Non-productive cough along with a febrile systemic illness are typically present in Q fever pneumonia. Although characteristically described as an ‘atypical’ pneumonia, it can be severe and sometimes fatal.
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Q fever notifications by year in Australia from 2010 to 2020. Data from National Notifiable Diseases Surveillance System, accessed April 2021.
• Chronic Q fever, also called persistent localised infection, can occur months or years after acute infection regardless of whether the acute infection was clinically apparent or asymptomatic. Patients with chronic Q fever typically have a febrile illness with non-specific symptoms, consistent with PUO (Pyrexia of Unknown Origin), with focal clinical manifestations that vary with the site of persisting infection. The cardiovascular system is the most common organ system implicated, with chronic Q fever endocarditis and vascular bed infections (e.g. mycotic aneurysm) both occurring. Persistent osteomyelitis can occur, with multi-focal osteomyelitis more characteristic in children. Less commonly a variety of focal organ system infections have been reported. • Post-infectious chronic fatigue-like syndrome is well- described and is thought to result from the ongoing presence of non‑viable Coxiella antigens causing persistent immune cytokine stimulation. • Infection in pregnancy, particularly during the first trimester, is associated with an increased likelihood of obstetric complications including intrauterine growth restriction and foetal death. • Q fever in humans is typically diagnosed with serology. For acute infection a single high phase 2 IgM titre is suggestive, however serology on paired acute and convalescent sera demonstrating a greater than fourfold increase in IgG titre is preferred. Patients with chronic Q fever will typically have raised phase 1 antibodies. Molecular diagnosis with PCR is increasingly being used, and may be performed on blood or tissues (e.g. infected valve tissue).
CONTENTS
65 Companion Animal Zoonoses Guidelines
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