For the answer, you need to find the source of the mannose.
Sharma, et al (2014) points out that
Mannose occurs in microbes, plants and animals. Free mannose is found in small amounts in many fruits such as oranges, apples and peaches  and in mammalian plasma at 50–100 μM . More often, mannose occurs in homo-or hetero-polymers such as yeast mannans (α-mannose) where it can account for nearly 16% of dry weight 
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So the mannose is actually coming from the candida yeast infection being studied by Monson & Wilkinson (1981).
Sharma et al. also points out that mannose has good, bad or ugly outcomes depending on its steady state levels and metabolic flux and their review describes the role of mannose at cellular level and its impact on organisms.
Mannose is a simple sugar with a complex life. It’s a welcome therapy for genetic and acquired human diseases, but it kills honeybees and blinds baby mice. It could cause diabetic complications. Mannose chemistry, metabolism, and metabolomics in cells, tissues and mammals can help explain these multiple systemic effects.
Monson, T. P., & Wilkinson, K. P. (1981). Mannose in body fluids as an indicator of invasive candidiasis. Journal of clinical microbiology, 14(5), 557–562. https://doi.org/10.1128/jcm.14.5.557-562.1981 (Open access at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC273987/)
Sharma, V., Ichikawa, M., & Freeze, H. H. (2014). Mannose metabolism: more than meets the eye. Biochemical and biophysical research communications, 453(2), 220-228. https://doi.org/10.1016/j.bbrc.2014.06.021 (Open access at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4252654/)