sharon sanders
Editor-in-Chief & President
Outbreak of Q fever among a group of high school students in Slovenia, March-April 2007
E Grilc<SUP>1</SUP>, M Sočan<SUP>1</SUP>, N Koren<SUP>1</SUP>, V Učakar<SUP>1</SUP>, T Av?ič<SUP>2</SUP>, M Pogačnik<SUP>3</SUP>, A Kraigher (Alenka.Kraigher@ivz-rs.si)<SUP>1</SUP>
1. Communicable Disease Centre, National Institute of Public Health, Ljubljana, Slovenia
2. Institute of Microbiology and Immunology, Faculty of Medicine, University of Ljubljana, Slovenia
3. Veterinary Faculty, University of Ljubljana, Slovenia
A group of 33 veterinary students and two teachers contracted a laboratory-confirmed Q fever infection during a training course on a sheep farm in Slovenia in March 2007. The disease is caused by Coxiella burnetii, an intracellular bacterium found worldwide in various species of farm and domestic animals.
Outbreak investigation
On 17 April 2007 the Communicable Disease Centre at the National Public Health Institute was informed about a case of Q fever in an 18 year-old student of a veterinary high school. The patient had developed high fever and a severe headache on 30 March 2007. Chest X-rays showed pneumonia. The student reported that her classmates in the same school year had been complaining about similar symptoms.
We suspected that the patient and her schoolmates might have been exposed to a common source of Q fever when attending a training course on a sheep farm (Farm A) located in the south-western part of Slovenia in March 2007 [1]. An epidemiological investigation was launched involving all third grade students of the veterinary high school.
Epidemiological and clinical data
The patient's high school year has 66 students. As part of their training, 45 of the students spent several hours between 5 and 23 March 2007 on Farm A, together with three teachers. They were trimming sheep?s feet, disinfecting wounds, and applying intramuscular vitamins and anti-helmintic injections as a preventive measure to healthy animals in a stable with approximately 500 sheep. Parturition time of the sheep on Farm A was from end of January to beginning of March this year.
We interviewed all individuals who had been at Farm A, and tested them for Q fever. In addition, 20 students who had not participated in the training course in March were included as a control group. One student from the control group had spent a short time on Farm A in autumn 2006. All interviewed individuals (68 altogether) had been in contact with different domestic animals at home and during school training courses at several locations.
Among 48 exposed individuals, there were 34 (71%) with high fever (38?C or more) with or without a headache. Four individuals (8%) had serious headaches only, but were not sure about fever, and three individuals (6%) reported symptoms of a common cold. Seven individuals (15%) were asymptomatic. The first person to develop symptoms of high fever and headache started to feel ill on 20 March 2007.
Among the 20 control subjects (including the student who had spent a short time on the sheep farm in autumn 2006), three students reported having a prolonged cough, and one had symptoms of a common cold. Sixteen (80%) students were completely asymptomatic.
Laboratory investigation
Serum samples were collected from 63 individuals (93% of the 68 interviewees) and sent to the Institute of Microbiology and Immunology, Medical Faculty in Ljubljana. They were tested by indirect immunofluorescence (FOCUS diagnostics) for the presence of IgG and IgM antibodies to C. burnetii phase I and II antigens.
A laboratory-confirmed case of acute Q fever was defined as an individual with IgM titres higher than 1:16 and/or IgG titres higher than 1:256.
Overall, the results confirmed acute Q fever in 36 individuals (57% of the 63 tested). Serum samples from 26 individuals (41%) were negative and the test result of one sample was inconclusive.
Of a total of 48 individuals who were exposed on Farm A in March 2007, 44 were tested and 35 of those (80%) were seropositive. They are shown in the Figure by date of onset of symptoms.
Eight exposed individuals (18% of 44 tested) were not infected, and one had an inconclusive result. In the control group, none was seropositive, except for one student who visited the sheep farm in autumn 2006. The serology results of exposed versus non-exposed individuals are summarised in the Table.
Among the 36 laboratory-confirmed cases (35 exposed in March 2007 and one exposed in autumn 2006), four were asymptomatic, while the other 32 (89%) suffered from high fever, headache, chills, muscle aches, sweating and nausea. Twenty-five patients (69%) consulted a physician, and three (8%) developed radiologically confirmed pneumonia. Although 13 cases (36%) were given antibiotic treatment, only six (16%) received adequate antibiotic therapy with doxycycline, quinolones or macrolide antibiotic. At the time the treatment was initiated, the laboratory results indicating Q fever infection were not known.
Conclusion
The data analysis showed a significant statistical correlation between a positive serological test for C. burnetii and attendance of the training course on the sheep farm in March 2007 (p value <0,001). There was no significant statistical correlation between a positive test and attendance of school training courses in other places or contact with domestic animals at the students? homes. We concluded that the sheep farm was the source of the Q fever outbreak.
Outbreak control measures
The first Q fever outbreak among humans in Slovenia was mentioned in 1954. Two outbreaks were described in 1985. The source of one was contact with a sheep herd; the other occurred among workers at a tannery, who were probably exposed through contact with sheep hides [2]. Further outbreaks due to contact with infected sheep were reported in 1991 and 1992 [3,4]. Between 1996 and 2005, between zero and five Q fever cases were notified in Slovenia [5].
The Communicable Disease Centre at the National Public Health Institute was collaborating with regional epidemiologists from Ljubljana and Koper, and with the veterinary high school and faculty of Ljubljana on the outbreak investigation. Further collaboration with the Department for Infectious Diseases and the Health Inspectorate at the Ministry of Health, and the Veterinary Office at the Ministry of Agriculture resulted in a cascade of public health and veterinary measures.
Public health measures [1]
References:
E Grilc<SUP>1</SUP>, M Sočan<SUP>1</SUP>, N Koren<SUP>1</SUP>, V Učakar<SUP>1</SUP>, T Av?ič<SUP>2</SUP>, M Pogačnik<SUP>3</SUP>, A Kraigher (Alenka.Kraigher@ivz-rs.si)<SUP>1</SUP>
1. Communicable Disease Centre, National Institute of Public Health, Ljubljana, Slovenia
2. Institute of Microbiology and Immunology, Faculty of Medicine, University of Ljubljana, Slovenia
3. Veterinary Faculty, University of Ljubljana, Slovenia
A group of 33 veterinary students and two teachers contracted a laboratory-confirmed Q fever infection during a training course on a sheep farm in Slovenia in March 2007. The disease is caused by Coxiella burnetii, an intracellular bacterium found worldwide in various species of farm and domestic animals.
Outbreak investigation
On 17 April 2007 the Communicable Disease Centre at the National Public Health Institute was informed about a case of Q fever in an 18 year-old student of a veterinary high school. The patient had developed high fever and a severe headache on 30 March 2007. Chest X-rays showed pneumonia. The student reported that her classmates in the same school year had been complaining about similar symptoms.
We suspected that the patient and her schoolmates might have been exposed to a common source of Q fever when attending a training course on a sheep farm (Farm A) located in the south-western part of Slovenia in March 2007 [1]. An epidemiological investigation was launched involving all third grade students of the veterinary high school.
Epidemiological and clinical data
The patient's high school year has 66 students. As part of their training, 45 of the students spent several hours between 5 and 23 March 2007 on Farm A, together with three teachers. They were trimming sheep?s feet, disinfecting wounds, and applying intramuscular vitamins and anti-helmintic injections as a preventive measure to healthy animals in a stable with approximately 500 sheep. Parturition time of the sheep on Farm A was from end of January to beginning of March this year.
We interviewed all individuals who had been at Farm A, and tested them for Q fever. In addition, 20 students who had not participated in the training course in March were included as a control group. One student from the control group had spent a short time on Farm A in autumn 2006. All interviewed individuals (68 altogether) had been in contact with different domestic animals at home and during school training courses at several locations.
Among 48 exposed individuals, there were 34 (71%) with high fever (38?C or more) with or without a headache. Four individuals (8%) had serious headaches only, but were not sure about fever, and three individuals (6%) reported symptoms of a common cold. Seven individuals (15%) were asymptomatic. The first person to develop symptoms of high fever and headache started to feel ill on 20 March 2007.
Among the 20 control subjects (including the student who had spent a short time on the sheep farm in autumn 2006), three students reported having a prolonged cough, and one had symptoms of a common cold. Sixteen (80%) students were completely asymptomatic.
Laboratory investigation
Serum samples were collected from 63 individuals (93% of the 68 interviewees) and sent to the Institute of Microbiology and Immunology, Medical Faculty in Ljubljana. They were tested by indirect immunofluorescence (FOCUS diagnostics) for the presence of IgG and IgM antibodies to C. burnetii phase I and II antigens.
A laboratory-confirmed case of acute Q fever was defined as an individual with IgM titres higher than 1:16 and/or IgG titres higher than 1:256.
Overall, the results confirmed acute Q fever in 36 individuals (57% of the 63 tested). Serum samples from 26 individuals (41%) were negative and the test result of one sample was inconclusive.
Of a total of 48 individuals who were exposed on Farm A in March 2007, 44 were tested and 35 of those (80%) were seropositive. They are shown in the Figure by date of onset of symptoms.
Eight exposed individuals (18% of 44 tested) were not infected, and one had an inconclusive result. In the control group, none was seropositive, except for one student who visited the sheep farm in autumn 2006. The serology results of exposed versus non-exposed individuals are summarised in the Table.
Among the 36 laboratory-confirmed cases (35 exposed in March 2007 and one exposed in autumn 2006), four were asymptomatic, while the other 32 (89%) suffered from high fever, headache, chills, muscle aches, sweating and nausea. Twenty-five patients (69%) consulted a physician, and three (8%) developed radiologically confirmed pneumonia. Although 13 cases (36%) were given antibiotic treatment, only six (16%) received adequate antibiotic therapy with doxycycline, quinolones or macrolide antibiotic. At the time the treatment was initiated, the laboratory results indicating Q fever infection were not known.
Conclusion
The data analysis showed a significant statistical correlation between a positive serological test for C. burnetii and attendance of the training course on the sheep farm in March 2007 (p value <0,001). There was no significant statistical correlation between a positive test and attendance of school training courses in other places or contact with domestic animals at the students? homes. We concluded that the sheep farm was the source of the Q fever outbreak.
Outbreak control measures
The first Q fever outbreak among humans in Slovenia was mentioned in 1954. Two outbreaks were described in 1985. The source of one was contact with a sheep herd; the other occurred among workers at a tannery, who were probably exposed through contact with sheep hides [2]. Further outbreaks due to contact with infected sheep were reported in 1991 and 1992 [3,4]. Between 1996 and 2005, between zero and five Q fever cases were notified in Slovenia [5].
The Communicable Disease Centre at the National Public Health Institute was collaborating with regional epidemiologists from Ljubljana and Koper, and with the veterinary high school and faculty of Ljubljana on the outbreak investigation. Further collaboration with the Department for Infectious Diseases and the Health Inspectorate at the Ministry of Health, and the Veterinary Office at the Ministry of Agriculture resulted in a cascade of public health and veterinary measures.
Public health measures [1]
- suspension of all student training courses and visits to the sheep farm;
- ban on selling dairy products from the sheep farm;
- improvement of sanitary conditions on the sheep farm;
- serological testing of farm employees;
- workplace risk reassessment (farm employees, forestry workers in the vicinity), in process;
- serological testing of students who had been trained on the sheep farm in 2007, final results expected;
- clinical and serological follow up of seropositive human cases, in process.
- serological testing of animals at the sheep farm (to date 60% seropositive animals);
- re-introduction of Q fever monitoring in small and large ruminants proposed by the Veterinary Chamber;
- vaccination of animals considered, vaccine procurement in process.
References:
- CNB novice, monthly CNB report, CDC, NIPH Slovenia: http://www.ivz.si/javne_datoteke/datoteke/1311-CNB_maj.pdf
- Epidemiolo?ko spremljanje nalezljivih bolezni v Sloveniji, Oddelek za epidemiologijo za leto 1985, CDC report, NIPH, Slovenia
- Epidemiolo?ko spremljanje nalezljivih bolezni v Sloveniji, Oddelek za epidemiologijo za leto 1991, CDC report, NIPH, Slovenia
- Epidemiolo?ko spremljanje nalezljivih bolezni v Sloveniji, Oddelek za epidemiologijo za leto 1992, CDC report, NIPH, Slovenia
- Epidemiolo?ko spremljanje nalezljivih bolezni v Sloveniji v letu 2005, CDC report, NIPH, Slovenia: http://www.ivz.si/javne_datoteke/datoteke/798-Epidemiolosko_spremljanje_NB_2005.pdf
- VURS, Veterinary Office at Ministry of Agriculture, Slovenia: http://www.vurs.gov.si/si/javne_objave/mrzlica_q/