The Rickettsiaceae, Anaplasmataceae, and Coxiellaceae

Organisms belonging to the families Rickettsiaceae, Anaplasmataceae, and Coxiellaceae are a diverse group of intracellular bacteria that cause a variety of infections in humans. As in the case of the Rickettsiaceae and Anaplasmataceae, hematophagous arthropod vectors play a role in maintaining the agents in nature and transmit the agents to cause disease. Coxiella burnetii, the sole pathogen of the family Coxiellaceae, is a zoonosis spread to humans by the inhalation of contaminated aerosols. In the last 2 decades, there has been an emergence of new rickettsial and ehrlichial species as well as new syndromes attributed to species previously deemed nonpathogenic. The growing list of pathogens and syndromic illnesses adds a layer of complexity to their recognition. Additionally, the clinical manifestations of infections caused by these agents are protean and nonspecific. For these reasons, establishing an accurate and timely diagnosis is often difficult. Therefore, knowledge of available laboratory tests, their interpretation, and their shortcomings is crucial for the management of infections caused by these bacteria.