Kampschreur Linda M, Oosterheert Jan Jelrik, Koop Annemarie M C, Wegdam-Blans Marjolijn C A, Delsing Corine E, Bleeker-Rovers Chantal P, De Jager-Leclercq Monique G L, Groot Cornelis A R, Sprong Tom, Nabuurs-Franssen Marrigje H, Renders Nicole H M, van Kasteren Marjo E, Soethoudt Yvonne, Blank Sybrandus N, Pronk Marjolijn J H, Groenwold Rolf H H, Hoepelman Andy I M, Wever Peter C
Division of Medicine, Dept. of Internal Medicine and Infectious Diseases, University Medical Center Utrecht, Utrecht, the Netherlands.
Clin Vaccine Immunol. 2012 May;19(5):787-90. doi: 10.1128/CVI.05724-11. Epub 2012 Mar 21.
Diagnosis of chronic Q fever is difficult. PCR and culture lack sensitivity; hence, diagnosis relies mainly on serologic tests using an immunofluorescence assay (IFA). Optimal phase I IgG cutoff titers are debated but are estimated to be between 1:800 and 1:1,600. In patients with proven, probable, or possible chronic Q fever, we studied phase I IgG antibody titers at the time of positive blood PCR, at diagnosis, and at peak levels during chronic Q fever. We evaluated 200 patients, of whom 93 (46.5%) had proven, 51 (25.5%) had probable, and 56 (28.0%) had possible chronic Q fever. Sixty-five percent of proven cases had positive Coxiella burnetii PCR results for blood, which was associated with high phase I IgG. Median phase I IgG titers at diagnosis and peak titers in patients with proven chronic Q fever were significantly higher than those for patients with probable and possible chronic Q fever. The positive predictive values for proven chronic Q fever, compared to possible chronic Q fever, at titers 1:1,024, 1:2,048, 1:4,096, and ≥1:8,192 were 62.2%, 66.7%, 76.5%, and ≥86.2%, respectively. However, sensitivity dropped to <60% when cutoff titers of ≥1:8,192 were used. Although our study demonstrated a strong association between high phase I IgG titers and proven chronic Q fever, increasing the current diagnostic phase I IgG cutoff to >1:1,024 is not recommended due to increased false-negative findings (sensitivity < 60%) and the high morbidity and mortality of untreated chronic Q fever. Our study emphasizes that serologic results are not diagnostic on their own but should always be interpreted in combination with clinical parameters.
慢性Q热的诊断较为困难。聚合酶链反应（PCR）和培养缺乏敏感性；因此，诊断主要依赖于使用免疫荧光测定法（IFA）的血清学检测。最佳的I期IgG临界滴度存在争议，但估计在1:800至1:1600之间。在确诊、疑似或可能患有慢性Q热的患者中，我们研究了血液PCR阳性时、诊断时以及慢性Q热期间峰值水平时的I期IgG抗体滴度。我们评估了200名患者，其中93例（46.5%）确诊，51例（25.5%）疑似，56例（28.0%）可能患有慢性Q热。65%的确诊病例血液中贝纳柯克斯体PCR结果为阳性，这与高I期IgG相关。确诊慢性Q热患者诊断时的I期IgG滴度中位数和峰值滴度显著高于疑似和可能患有慢性Q热的患者。与可能患有慢性Q热相比，确诊慢性Q热在滴度为1:1024、1:2048、1:4096和≥1:8192时的阳性预测值分别为62.2%、66.7%、76.5%和≥86.2%。然而，当使用≥1:8192的临界滴度时，敏感性降至<60%。尽管我们的研究表明高I期IgG滴度与确诊慢性Q热之间存在密切关联，但由于假阴性结果增加（敏感性<60%）以及未经治疗的慢性Q热的高发病率和死亡率，不建议将当前诊断的I期IgG临界值提高到>1:1024。我们的研究强调，血清学结果本身并不能作为诊断依据，而应始终结合临床参数进行解释。
