Serological challenges in the diagnosis of chronic Q fever

L.M. Kampschreur1,2, J. J. Oosterheert1, A.M.C. Koop1, M. C.A. Wegdam-Blans4, C.E. Delsing4, C.P. Bleeker-Rovers4, M.G.L. De Jager-Leclercq5, C.A.R. Groot6, T. Sprong4,7,8, M.H. Nabuurs-Franssen8, N.H.M. Renders9, M.E. van Kasteren10, Y. Soethoudt11, S.N. Blank12, M.J.H. Pronk13, R.H.H. Groenwold14, A. I.M. Hoepelman1, P.C. Wever9

1Division of Medicine, Dept. of Internal Medicine and Infectious Diseases, University Medical Center Utrecht, 2Dept. of Internal Medicine, Jeroen Bosch Hospital, ’s-Hertogenbosch, 3Lab. for Medical Microbiology, PAMM foundation, Veldhoven, 4Dept. of Internal Medicine, Division of Infectious Diseases, Radboud University Nijmegen Medical Center, Nijmegen, 5Dept. of Internal Medicine, Bernhoven Hospital, , 6Dept. of Pulmonology, Bernhoven Hospital, Oss, 7Dept. of Internal Medicine, Canisius-Wilhelmina Hospital, Nijmegen, 8Dept. of Medical Microbiology and Infectious Diseases, Canisius-Wilhelmina Hospital, Nijmegen, 9Dept. of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, ’s-Hertogenbosch, 10Dept. of Internal Medicine, St. Elisabeth Hospital, , 11Dept. of Internal Medicine, Elkerliek Hospital, 12Dept. of Internal Medicine, Maxima Medical Center, /Veldhoven 13Dept. of Internal Medicine, Catharina Hospital, Eindhoven, 14Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht. Email: [email protected]

Introduction and Purpose

After primary infection with Coxiella burnetii, 1-5% of patients develop chronic Q fever. Endocarditis and infection of a vascular prosthesis or aortic aneurysm are the most important manifestations. Since PCR and culture on blood have low sensitivity for detection of chronic Q fever, diagnosis relies mainly on serologic tests, of which immunofluorescence assay (IFA) is most commonly used. Cut-off titers for phase I IgG to detect chronic infection are estimated between 1:800 and 1:1600. We studied the serological profiles in patients with established chronic Q fever.

Methods IgG phase I Se (%) Sp (%) PPV (%) NPV (%) 1:1024 97.8% nd 62.2 nd • We selected all patients included until September 1:2048 94.6% 21.4% 66.7 70.6 2011 in the Dutch National Database of Chronic Q 1:4096 80.6% 58.9% 76.5 64.7 Fever Patients. 1:8192 60.2% 83.9% 86.2 55.9 • Patients were categorized as proven, probable and 1:16384 47.3% 94.6% 93.6 52.0 possible, according to Dutch consensus guidelines ≥1:32786 25.8% 96.4% 94.4 47.8 • We examined phase I IgG antibody titers (IFA, using Focus Diagnostics) at time of diagnosis, at Table 1. Test characteristics of phase I IgG cut-off (peak) titers for diagnosis of chronic Q fever compared to possible chronic Q fever peak levels and at time of PCR analysis on blood

phase I IgG titer Results >=1:32768 at diagnosis phase I IgG peak titer • 200 patients were included: 1:16384 • 93 (46.5%) proven chronic Q fever 1:8192 scale)

• 52 (55.0%) PCR+ in blood 2

• 10 (10.8%) PCR+ in tissue 1:4096 • 13 (13.9%) PCR+ in blood and tissue • 51 (25.5%) probable chronic Q fever 1:2048 • 56 (28.0%) possible chronic Q fever 1:1024 Phase I IgG (log

20 1:512 PCR negative PCR positive 15 proven probable possible chronic Q fever chronic Q fever chronic Q fever Figure 2. Median phase I IgG titers at diagnosis and peak titer are 10 significantly higher in proven chronic Q fever (both 1:8192, p<0.05), compared to probable (1:2048 and 1:4096) and possible chronic Q 5 fever (both 1:2048) Number patients of

0 Conclusion 4 8 6 2 8 2 4 9 09 High phase I IgG titers are strongly associated with 1:512 :10 4 1 1:20 1: 1:81 :3276 1:16384 proven chronic Q fever, especially when > 1:4096 >=1 Phase I IgG titers (PPV >86%). Due to low sensitivity of these titers (<60%) and high morbidity and mortality of untreated Figure 1. Each increase of phase I IgG titre gave a significant rise chronic Q fever, increasing the current phase I IgG in probability of positive C. burnetii PCR on blood in proven chronic Q fever patients (OR 1.35, 95%CI 1.02-1.77, p = 0.033) cut-off is not recommended. Serologic results should be interpreted in combination with PCR and clinical parameters.

Participants Dutch National Q Fever Database