Table 1.

Specificity of Q fever IgM ELISA and CFT with IgM IFAT as the reference methoda

Disease state (IgM IFAT negative)No. of negative results/no. of IgM IFAT-negative sera (%)
ELISACFT
Positive RF3/4 (75)2/4 (50)
M. pneumoniae infection6/6 (100)6/6 (100)
C. psittaciinfection5/5 (100)3/3 (100)b
Leptospirosis3/5 (60)5/5 (100)
Legionellosis4/4 (100)4/4 (100)
IgM IFAT negativec 85/97 (88)87/97 (90)
Total IgM IFAT negative106/121 (88)107/119 (90)
  • a The IgM IFAT positive sera included 43 single sera positive by IgM IFAT and 5 S1 and 22 S2 sera from patients with Q fever. The sensitivity (positive results/IgM IFAT-positive sera) was as follows: ELISA, 69/70 (99%); CFT, 51/70 (73%).

  • b Two sera from patients with C. psittaci infections were not included in CFT analysis due to insufficient quantity of serum.

  • c The 97 negative IgM IFAT sera include the 80 single sera from patients found not to have Q fever on the basis of a negative IgM IFAT result and the 17 IgM IFAT negative acute-phase samples of serum pairs from patients diagnosed with Q fever.