Performance of the diagnostic test for Demodex spp. in the context of minimizing the risk of false negative results

Demodex species are permanent parasites of pilosebaceous units infesting humans worldwide. Of the two species associated with the human host, Demodex folliculorum is much more commonly detected and occurs more abundantly in hair follicles and Zeiss glands. Demodex brevis, on the other hand, is mainly associated with the sebaceous and meibomian glands, all over the body. The infestation is usually chronic, and the troublesome ocular and skin symptoms often make it difficult for patients to function in both a social and professional context. Despite this, diagnostics for Demodex spp. are still not routinely performed during ophthalmological and dermatological examinations. We aimed to compare preparations of eyebrow hair, eyelashes, and skin scrapings, and to investigate the correlation with false negative results in the laboratory diagnosis of demodicosis. Direct microscopic examination was applied on 100 patients (81 women and 19 men). The most common ocular and skin symptoms reported by the study participants were eyelid itching and erythema, respectively. Significant differences were found between infested and uninfested patients with regard to the following symptoms: eyelid itching which was more common in infested patients (35.8%) (p = 0.0343) and chalazion occurring only in infested patients (13.2%) (p = 0.0285). The collection of diagnostic material from more than one site e.g. nasolabial folds, eyebrow hairs or eyelashes has a significant effect on the test result. Taking a single type of a sample from a single face zone can lead to false negative results.