SHORT REPORT: SEROPREVALENCE OF HUMAN INFECTION BY COXIELLA BURNETII IN BARCELONA (NORTHEAST OF SPAIN) NEUS CARDEÑOSA, ISABEL SANFELIU, BERNAT FONT, TOMÁS MUÑOZ, MARÍA MERCEDES NOGUERAS, AND FERRAN SEGURA* Infectious Diseases Program, Department of Internal Medicine, Corporació Parc Taulí, Sabadell, Barcelona, Spain; UDIAT Diagnostic Center, Corporació Parc Taulí, Sabadell Barcelona, Spain; Department of Pediatric, Corporació Parc Taulí, Sabadell Barcelona, Spain Abstract. Coxiella burnetii is the causal agent of Q fever, a worldwide-distributed zoonosis, which is endemic in Spain. C. burnetii has an extensive reservoir, including farm animals and pets. The aim of this study was to determine the seroprevalence of C. burnetii in humans in Vallés Occidental (Barcelona, northeast of Spain) and its possible related risk factors. The prevalence of phase II antibodies from 216 subjects was determined by indirect immunofluorescence assay (IFA). Age, sex, living place, occupation, and contact with animals were surveyed. A 15.3% seroprevalence was found ( 1/40), and 8.8% of samples had titers  1/80. Seropositive cases were significantly higher in patients > 44 years of age. No statistically significant correlation was found between seropositivity and the remaining variables studied. Therefore, infection by C. burnetii seems to be endemic in our region, with a prevalence ranging from 9% to 15%, depending on the titers that are to be considered significant. Coxiella burnetii is an obligate intracellular, small, gram- negative bacterium. This microorganism is the causal agent of Q fever, a worldwide distributed zoonosis considered a public health problem in many countries. C. burnetii has an exten- sive reservoir, including many wild and domestic mammals, birds, and arthropods such as ticks. 1 The most frequent sources of human infection are farm animals, especially cattle, goats, and sheep. It has been shown that infected cats, rabbits, and dogs can also transmit C. burnetii to humans. 2,3 Animals are often chronically infected, shedding bacteria in feces, milk, urine, and especially, birth products of mammals. The aerosol route is the primary mode of human infection. 1 Contamination by aerosols may occur mainly from parturient fluids. The organism may be spread by the wind 4 ; therefore, patients without any contact with animals could be infected. Ingestion (raw eggs and mainly, drinking raw milk) 3 and per- son-to-person transmission (e.g., contact with parturient women, blood transfusion, autopsies, sexual transmission) 5 are minor routes. C. burnetii is resistant in adverse conditions and can survive for months to years in a sporelike state, con- taminating water or soil. In humans, Q fever presents as a clinical polymorphism and usually is asymptomatic (∼60% of the infections are asymp- tomatic seroconversions) 1 or mild, as a flu-like disease with spontaneous recovery. 1 The infection has two forms in hu- mans: acute and chronic. In the acute form, clinical manifes- tations such as pneumonia, prolonged fever, and granuloma- tous hepatitis occur. 6,7 The most frequent clinical manifesta- tion of the chronic form is endocarditis. 1 The acute form is often underdiagnosed because of a non-specific clinical pic- ture, and thus serology is extremely important in the diagno- sis of the disease. 1 Seroprevalence studies have a 2-fold interest: epidemio- logic and diagnostic. The first shows the prevalence in a given geographical area. The second allows for adjusting the cut-off point of the serologic titers for diagnostic purposes in the study region. The aim of this was to determine the seroprevalence of C. burnetii infection in a representative sample of 391,546 inhab- itants from a region where our hospital is a reference facility. The study was undertaken in Vallés Occidental (Barce- lona), a predominantly urban county near the coast in the northeast of Spain. A total of 11 municipalities (391,546 in- habitants) participated in the study. Two hundred sixteen serum samples from patients who had attended at Sabadell Hospital were collected during a 5-month period from September to January. The sample in- cluded adults undergoing minor surgery and children cared for at the Pediatrics Emergency Service for non-infectious diseases. Informed consent was obtained from all adult par- ticipants and from parents or legal guardians of minors. Taking into account the actual population of Vallés Occi- dental, the study population was stratified by age (0–14, 15– 29, 30–44, 45–64, and > 64 years) and by living place (rural: < 5,000 inhabitants, semi-urban: 5,000–50,000 inhabitants, ur- ban: > 50,000 habitants). For each study subject, the following variables were surveyed: age, sex, place of residence, contact with wild animals, contact with farm animals, contact with pets, and occupation. Those inhabitants unable to answer the epidemiologic survey were excluded. Sera were studied by indirect immunofluorescence, using a commercially available antigen (Coxiella burnetii spot IF; Bio-Mérieux, Marcy L’Étoile, France) obtained from Vero cell cultures infected with C. burnetii (phase II antigen). An- tibody determination was made by double serial dilutions, beginning with a 1/20 sampling dilution, and using a fluores- cein-labeled IgG immunoglobulin. The technique was con- ducted according to the manufacturer’s recommendations. Ti- ters  1/40 were considered positive. Data were analyzed with the SPSS package using Student t test to compare quantitative variables. Univariate group com- parisons were performed using  2 and Fisher exact test. A P < 0.05 was considered significant. Of the 216 subjects, 117 (54.16%) were men and 99 (45.84%) women. The age ranged from 0 to 91 years. Subjects were reported by 11 towns, and 149 (68.98%), 51 (23.61%), and 16 (7.41%) subjects lived in urban, semi-rural, and rural areas, respectively. In the group of 161 adults (> 18 years), there were 11 (6.8%) students, 27 (16.8%) retired, 37 (23%) * Address correspondence to Ferran Segura, Infectious Diseases Pro- gram, Department of Internal Medicine, Corporació Parc Taulí, Parc Taulí s/n, Sabadell, 08208 Barcelona, Spain. E-mail: fsegura@cspt.es Am. J. Trop. Med. Hyg., 75(1), 2006, pp. 33–35 Copyright © 2006 by The American Society of Tropical Medicine and Hygiene 33