Table 1.

Array of possible results using the GeneXpert multiplex assay for MPX detection^*

GeneXpert test interpretation	MPX assay	OPX assay	IAC assay
MPX positive	Positive	Positive	Positive/negative*
MPX negative	Negative	Positive/negative	Positive/negative
OPX positive	Positive/negative	Positive	Positive/negative
MPX, OPX negative	Negative	Negative	Positive
Negative through inhibition	Negative	Negative	Negative

IAC = internal amplification control; MPX = monkeypox, OPX = orthopoxvirus.

^*In multiplex assays, reaction components are shared competitively between separate polymerase chain reaction tests in the multiplex. The IAC template is limited to a low, but reliably amplifiable level to test for sample quality and inhibition for MPX- and OPX-negative cases. However, in samples of poor quality (demonstrated by high MPX and/or OPX assay Ct values), the IAC may amplify though still yielding a MPX- and/or OPX-positive test result.