Intestinal parasitic infections are a reality, and it is of great importance to find the correct way to diagnose them to avoid further disease transmission and chronic illnesses. Although for many years, parasitic infections are still neglected in terms of laboratory development. Still nowadays, microscopic examination of stool samples for the detection of cysts, trophozoites and ova remains the diagnostic method of choice for many laboratories; however, the method requires technical expertise, and it is laborious; it can also have low sensitivity with low levels of infection and time consuming (McHardy et al., 2014). The limitations of microscopy and antigen detection tests have influenced parasitologists towards the use of genomic amplification methods made possible with the advent of the molecular diagnose but it is still remain underused (Won et al., 2016). Step by step antigen detection tests for G. lamblia, Cryptosporidium spp and Entamoeba hystolitica have been widely introduced in the day-to-day laboratory workflow especially in those laboratories with lower capacities for parasitic diagnosis and they are associated with a significant improvement (McHardy et al., 2014) and even, there are several tests cleared by the FDA.
Although growth in international travel and migration from endemic areas, in our settings G. lamblia and E.vermicularis are still the most prevalent pathogens. In high throughput laboratories, tools for detection of these parasites are mandatory. The results obtained for the G. lamblia diagnosis suggest that SediMAX2® could be a good tool and it can be implemented for the detection of this protozoon (SE, SP, PPV and NPV for G. lamblia; 89,29%; 98,15%; 98,68%; 85,48%, respectively). Out of the 84 samples positives for G. lamblia, in 9 cases SediMAX2® was not able to detect them. In the other hand, it is important to remember that a negative result does not rule out parasitic infection because several parasites (particularly G. lamblia) have an intermittent shedding (CLSI, 2005) and the probability of parasite detection increases more than 95% when 3 stools are tested (Marti and Koella, 1993), so a serial parastilogical studies are still needed to confirm a high suspicion of G. lamblia infection in case of a previous negative result. For the rest of protozoa SediMAX2® was able to detect the protozoa with a pathogenic role, but only 4 E.hystolitica/dispar were included in the study.
In case of worm infections, all eggs were properly identified with the exception of E. vermicularis in all three cases, 2 A. lumbricoides and 1 case of S. stercoralis larvae. In the rest 15 worm infections from 13 patients, all eggs were detected. The discrepancies in the worm infections must be explained by the fact that in case of E. vermicularis, stool wet mount examination is not the recommended tool for the diagnosis and, even the presence in the microscopic mount, a tape slide-test must be sent to the laboratory to a correct diagnosis. For S. stercoralis, it is known that the visualization of rhabditiform larvae in stools in not always possible and complemented techniques (parasitological or serology-based test) is needed. Diagnosis of S.stercoralis, is often delayed due the presence of subclinical or poorly-symptomatic cases and the usually low parasite load and irregular larvae output. This fact makes that this worm is also known as there is but not seen (Montes et al., (2010).
The most remarkable fact in this automatic microscopic system is the reducing in hand and microscope time. With the possibility of a big storage of images, this system could reduce the time in microscope with a high positive predictive value.
Parasitic diagnosis is heavy workload and relies exclusively on the experience of the trained technicians. Thus, it is difficult to maintain enough people with expertise in diagnostic medical parasitology. A recognized image system based in the same principle that urines must be developed by the biomedical engineering to provide new tools in case of intestinal parasitic infections. Additionally, the improvements in the sample process to avoid detritus that can difficult the interpretation of the images would help to better parasitological diagnose.
This study is a first step to implement engineering with medical practice to help medical microbiologist diagnose their patients. There is still an opportunity for improvement, especially with high throughput laboratories and when diagnosis is almost exclusively manual. A two-step algorithm including antigen detection and digital microscopic could be useful to help parasitologists in their day-to-day workload.
This study was partially funded by Menarini, S.A., distributor of SediMAX2® in Spain. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.