An infectious disease or disorder in a fluid, such as a mammalian blood sample, is detected by taking a transmission spectrum of a test sample in at least a portion of the ultraviolet visible near-infrared and comparing the spectrum with a standard sample spectrum. From the comparison it is then determined whether the fluid from the test sample contains an infectious disease or disorder, and an identity of the infectious disease or disorder is determined. Spectroscopic and multiwavelength turbidimetry techniques provide a rapid, inexpensive, and convenient means for diagnosis. The comparison and determination steps may be performed visually or by spectral deconvolution.