Table 5.

Clinical significance of an IgM/IgG serological test result.

Phase of Infection	Type of Test
	PCR	IgM	IgG
The window period for a test designed to detect a specific disease	P(+)	N(−)	N(−)
Early stage of infection	P(+)	P(+)	N(−)
Active phase of infection	P(+)	P(+)	P(+)
Late or recurrent stage of infection	P(+)	N(−)	P(+)
Early stage of infection. PCR result may be false negative *	N(−)	P(+)	N(−)
Past infection (recover) *	N(−)	N(−)	P(+)
The recovery stage of infection, or PCR result may be false negative *	N(−)	P(+)	P(+)
No infection and no special symptoms	N(−)	N(−)	N(−)

P(+)—positive; N(−)—negative. * Human coronaviruses (HCoV) OC43, 229E, NL63, and HKU1 may cause false positive ELISA results.