TABLE 5.

Diagnosis of variola by laboratory tests^a

Stage	Material used	Microscopic examination (1 h)	Detection or isolation of of virusb (1 to 3 days)	Antigen detectionc (3 to 24 h)	Detection of antibodiesd (3 h to 3 days)
Preeruptive	Blood		±	±	−
Maculopapular	Blood		±	±	±
	Skin lesions	+	+	+
	Saliva		+
Vesicular	Blood		±		+
	Skin lesions	+	+	+
Pustular	Blood				+
	Pustular fluid	±	+	+
Crusting	Blood				+
	Crusts	−	+	+

^aThe time required for completion of each test is given. Results: +, usually positive; −, usually negative; ±, positive or negative. 

^bCulture on chorioallantoic membrane of chicken embryos or in tissue culture. 

^cComplement fixation, agar gel precipitation, or immunofluorescence. 

^dHemagglutination inhibition, complement fixation, or neutralization. Antibodies may appear earlier in previously vaccinated patients. +, rise in antibody titer.