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Introduction

The estimated case fatality rate is < 2% of hospitalized patients (wikipedia)

Animal and human

Transmission / Exposure Route

Infection of humans usually occurs by inhalation of these organisms from air that contains airborne barnyard dust contaminated by dried placental material, birth fluids, and excreta of infected animals

Case Fatality Ratio

The estimated case fatality rate is low, at 1-2% of hospitalized patients.[1]

Incubation Period

The acute symptoms usually develop within 2-3 weeks of exposure, although as many as half of humans infected do not show symptoms[2]

Burden of Disease

Q Fever became a reportable disease in the United States in 1999. Between 2000 and 2004, the US saw an average of 51 cases every year. In 2005, 136 cases were reported to the CDC, and 169 in 2006.[3]
The annual has been reported as 0.28 cases per million persons[3]
Internationally, prevelance is estimated from 5% in urban areas to 30% in rural areas. This is likely an underestimate due to asymptomatic infections. Results of serological testing of blood donors revealed a prevalence of 18% to 37% in Africa. The United Kingdom sees approximately 100 cases of Q Fever a year[4]

Duration of infectiousness and disease

Q fever is rarely contagious between humans.[1]
Acute illness responds well to antibiotic treatment, and fevers usually resolve in an average of 4.3 days[1]
Chronic illness is less common, but can develop if an acute illness is not treated quickly. Endocartitis accounts for 60-70% of chronic Q fever and is the most common cause of fatality of the illness.[1]

Symptomology

Most patients (50-60%) infected with Q fever are asymptomatic. Those who do show symptoms present flu-like symptoms including fevers, coughs, sweats, myalgias, and arthralgias. Other possible symptoms are pneumonia and hepatitis.[5]

Immunity

Live, whole-cell, and acellular vaccines have been developed for Q fever.[1]

Microbiology

Obligate intracellular small Gram-negative bacteria

Enviromental Survival

The organism is extremely hardy and resistant to heat, drying, and many common disinfectants which enable the bacteria to survive for long periods in the environment

Route: intraperitoneal, Response: death

beta-Poisson

$$P(response)=1-[1+dose\frac{2^{\frac{1}{a}}-1}{N^{50}} ]^{-a}$$

a = 3.57E-01
N50 = 4.93E+08
LD50 = 4.93E+08

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NCBI Publications on Risk Assesment:

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