Table 3.

Case definition on the bases of the diagnostic test results

Confirmed	PCR positive and/or IgM positive plus PRNT positivea, and/or seroconversion or four fold increase in neutralizing antibody titers in two consecutive samples.
Probable	IgM positive plus PRNT border lineb in acute samplesc.
Possible	IgM negative and PRNT positive/border line, or IgM positive but PRNT negative in acute samples.
Not confirmed	IgM positive and PRNT negative in late/convalescent samples, or PRNT positive without an increase in the titer in two consecutive samples.

^aPRNT80 ≥ 10: positive

^bPRNT50 ≥ 10: border line (b.l.)

^cThese cases were classified as possible if PRNT b.l. results were obtained toward different viruses