Chronic Q fever: relevance of serology.

To the Editor—We read with interest the recent paper on Q fever by Healy et al [1], which describes the results of initial and follow-up serologic analysis after an outbreak of Q fever, and the discrepancy in test results obtained from different reference laboratories. This article raises the problem of management of asymptomatic patients with a chronic serological profile (phase 1 serum level of immunoglobulin G [IgG], $800 mg/dL). We conducted a retrospective analysis of 35 patients with chronic Q fever whose conditions were followed in our institution between 1996 and 2009, who had an initial (n 5 26) or secondary (postacute phase) (n 5 9) serological diagnosis of chronic Q fever. Of the 35 patients, 23 were asymptomatic, 9 had definite endocarditis (Duke criteria), 2 had hepatitis, and 1 had optical neuritis. The asymptomatic patients included 7 with possible cases of endocarditis, according to the Duke criteria (phase 1 IgG level, $800 mg/dL and valvular disease). Of the 16 (n 5 23 minus 7) asymptomatic patients with a chronic serological profile, 9 received no treatment; all 9 were healthy. Clinical and serological controls were conducted in 2010 for 7 of these patients: 5 had a healing serological profile and 2 had serological controls (follow-up ,1 year) that showed a regression of the phase 1 IgG or IgA titers.