الفهرس 
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Abstract
B. hominis is a unicellular eukaryotic, it is an obligatory non-aerobic protozoan found in the colon of different hosts including humans. It is characterized by its polymorphic appearance, including a great variation in size from 5 to 50 um. It is one of the most common parasites found in any stool survey. The prevalence of B. hominis in developed and developing countries was reported to be 10% and 50% respectively. Higher rates of B. hominis infection were recorded among patients from Alexandria, Egypt suffering from irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) (52.5% and 65% respectively). Limited researches were available on its association with colorectal cancer.
Colorectal cancer is the third common neoplasm worldwide after lung and breast cancers. Worldwide over than 1 million individuals suffered from colorectal cancer per year, causing about 715,000 deaths in 2010. The world burden was expected to rise by 60% by year 2020 to reach more than 2.2 million new cases and 1.1 million deaths.
The aim of the present study was to investigate the possible association between
B. hominis and colorectal cancer among patients admitted to the endoscopy units and the possible risk factors in comparison to controls.
Stool samples were collected from patients admitted to colonoscopy units of different hospitals and from apparently healthy individuals during the period from June 2018 till March 2020. Samples from 86 colorectal cancer patients, 112 individuals with other gastrointestinal diseases and 121 controls were examined for diagnosing B. hominis infection and estimating its intensity of infection. Each Stool sample was examined microscopically as direct wet mount (saline/ iodine), as a trichrome stained smear and after concentration with Formal ether sedimentation technique. The stool sample was also cultured using Jones medium.
An interviewing questionnaire has been also designed to collect data on some sociodemographic factors, source of water, some food habits and medical history from colorectal cancer cases and controls.
from this study, the following results were obtained:
1- About 62% of colorectal cancer patients were aged from “45 to less than 65 years” old and only 17.5% of them were aged from “65 to 85 years” old but the difference was not statistically significant. About 56% of CRC patients were females.
2- Concerning the educational level, more than half of both cases and controls was illiterate or just reading/ writing level (58.1% & 52.9% respectively).
3- Only 26.7% of the cases and 41.3% of controls had jobs, the difference was statistically significant.
4- Only 46.6% of cases were drank water without filters while 9.3% of them used mineral water versus 62.8% and 0.8% of controls respectively, the difference was statistically significant (P=0.018, P=0.004 respectively). The percentage of alcoholics in the case group was double that in the control group; however, the difference was not statistically significant (P=0.325).
5- About 61% of cases and 40.5% of controls ate processed meat as sausage or luncheon and processed meat consumers were 2.2 times at higher risk to get colorectal cancer compared to non-consumers (p=0.005).
6- In spite of finding that the majority of cases and controls (94.2%, 85.1% respectively) gave history of consuming green leafy vegetables, the infrequent consumption of these vegetables was about two times (OR=1.848, P=0.041) riskier to cause CRC.
7- Clinical symptoms including change in bowel habits (either repeated diarrhea or prolonged constipation), passage of fresh blood with stool, repeated colic’s, loss of weight, nausea and vomiting were recorded for a statistically higher percentage of colorectal cancer cases compared to controls (P<0.001). On the other hands, no significant difference between CRC cases and controls as regards previous parasitic infections nor familial history of GIT diseases.
8- Considering pooled data of the techniques used, the total rate of B. hominis infection among the 319 samples examined was 34.2% and its intensity of infection (expressed as mean cyst count/30 HPF + SD) was 17.51 + 13.10.
9- The highest rate of B.hominis infection was detected among colorectal cancer cases (60.5%, P<0.001) followed by patients suffering from Crohn’s disease (36.4%, FEP= 0.481) while control individuals presented with a rate of 25.6% only.
10- CRC cases and those suffering from Crohn’s diseases presented with the highest mean cyst counts (20.77 ± 15.17, 21.75 ± 4.35 cyst / 30 HFP respectively), while a low count was recorded for controls (14.55 ± 10.89 cyst / 30 HPF). The difference was statistically significant.
11- B. hominis was the most prevalent parasite in both cases and controls, followed by Giardia lamblia and Entamoeba coli. The rates of these parasites were significantly higher among cases compared to controls.
12- CRC patients suffering from blastocytosis were about three times (OR=2.926, P=0.017) more likely to be simultaneously infected with other parasites than Blastocystis positive controls. The highest rate of co-infection was observed with Giardia lamblia followed by Entamoeba coli and Entamoeba histolytica.
13- Old CRC patients (65 years and more) presented with the highest rate of B. hominis infection (66.7%). On the other hand, controls of the same age group had the lowest rate of infection (21.4%) and the highest rate (26.9%) was detected among the age group ” 45- less than 65years”.
14- About 68% of CRC males and 54.2% of CRC females were found infected with B. hominis but without any significant difference. Meanwhile, females in the control group were slightly more infected with B. hominis than males (26.6% vs 24.6%).
15- There wasn’t any statistically significant association between B. hominis infection and levels of education in either cases or controls. Meanwhile, statistically significant higher rates were detected among illiterates and highly educated cases (64% each) compared to illiterates and highly educated controls (20.3% & 32. 5%), (P<0.001, P=0.013).
16- No significant association was found between rates of B. hominis infection and the work carried out by either colorectal cancer patients or controls. Those not working in both groups suffered from high rates of infection (69.6%, & 26.3% respectively).
17- Source of drinking water, food habits and personal hygiene were not statistically associated with B. hominis infection rate in both colorectal cancer cases and controls.
18- There wasn’t any significant association between the different complaints and B. hominis among both cases and controls. Meanwhile, higher rates were recorded among individuals of both groups who gave history of previous parasitic infections compared those who were not previously infected with parasites (80.0% & 28.6% respectively vs 59.3 & 25.4 respectively).
19- Most of cancer originated from the colon (53 out of 86: 61.6%) while only 27 of them (31.4%) originated from the rectum and 4 (4.7%) from the anal canal. Moreover. The highest percentage of colorectal cancer patients were diagnosed with grade II (58/86: 67.4%) and stage III cancers (39/86: 45.3%).
20- Patients with sigmoid colon cancer presented with a high rate of B. hominis (78.6%) and they were heavily infected (25.0 ± 15.26 cysts /30HPF).
21- Patients with stage I cancer presented with the highest rate of B. hominis (77.8%) but with the lowest mean cyst count (17.57 + 12.26 cysts/30 HPF). Meanwhile, patients with stage IV cancer showed the lowest rate of infection (56.7%) but with the highest mean cyst count (23.76 + 17.33 cysts /30HPF). The differences in infection rates and intensities were not statistically significant.
22- The multivariate logistic regression analysis indicated that only the intensity of B. hominis infection was the strongest risk factor for developing colorectal cancer (OR=1.064; 95%C.I.= 1.006- 1.126; P=0.30).
23- Direct wet mount had the lowest performance in detecting B. hominis (3.4% positive cases) followed by culture and formol ether (19.4% & 20.1% respectively), while trichrome was the best technique in diagnosing positive cases (29.5%). In comparison to the gold standard test (34.2%), the differences in detection rates were statistically highly significant (P< 0.001).
24- Among the four techniques used, for diagnosis of B. hominis, trichrome stain test showed the highest sensitivity (86.24%). Its specificity was 100%. It had a very good agreement with the gold standard as Cohen’s kappa coefficient (K) was 0.892. On the other hand, Jones’ culture had a sensitivity of 56.88%, a specificity of 100%. Cohen’s Kappa coefficient (K) was 0.635 indicating that the agreement between it and the gold standard was only good.
6.2. Conclusion
1- No significant association was detected between either age, sex or educational levels and colorectal cancer.
2- Working was significantly associated with a lower risk of developing colorectal cancer.
3- Mineral water consumers were at much higher risk to get colorectal cancer compared to tap water consumers.
4- Eating processed meat was a risk factor for developing CRC (OR= 2.247, P= 0.005).
5- Frequent consumption of green leafy vegetables for more than two times weekly was a protective factor against CRC development.
6- Change in bowel habits (either repeated diarrhea or prolonged constipation), passage of fresh blood with stool, repeated colic, loss of weight and nausea & vomiting were the symptoms highly associated with CRC.
7- Out of the 319 samples examined 109 (34.2%) were positive for B. hominis and the intensity of infection (expressed as mean cyst count/30 HPF + SD) was (17.51 + 13.10 cyst/ 30 HPF).
8- Patients with colorectal cancer were 4.4 times more likely to be infected with B. hominis than controls (p<0.001). They were also more heavily infected compared to controls (21.75 ± 4.35 cysts /30 HPF vs 14.55 ± 10.89, P=0.048 cyst /30 HPF).
9- Multiplicity of infection among CRC cases was significantly higher than among controls (100% vs 87%, P=0.017), mainly B. hominis and Giardia lamblia co-infection.
10- The difference in rates of B. hominis infection between the different age groups was not statistically significant in either cases or controls.
11- There wasn’t any statistically significant difference in B. hominis rates of infection between sex in both groups.
12- There was no significant association between the different socio-demographic risk factors, source of water, food habits or hygienic habits and B. hominis infection among both colorectal cancer cases and controls.
13- There was no statistical difference in B. hominis infection rates, or its mean cyst count as regards the tumor location, tumor grading or tumor staging.
14- Only, B. hominis intensity of infection was found to be the strongest risk factor for developing colorectal cancer (P=0.049, OR =1.060).
15- Out of the four techniques used, trichrome staining had the best performance. It showed the highest rate of B.hominis detection, highest intensity and sensitivity, and a very good agreement with the gold standard.
6.3. Recommendations
from the present study the following could be recommended:
1- Training technicians for better microscopic detection of B. hominis which could be confused with fat globules and yeast.
2- All CRC patients and even all susceptibles for developing CRC should be screened for B. hominis infection. Positive individuals should be treated.
3- The use of more than one diagnostic technique to detect intestinal parasites including B. hominis is still mandatory especially in low intensity settings and when evaluating the effect of treatment or a control program.
4- Modifying some of the conditions of Jones’ culture as by using a Ph of 7.5 could improve the yield of the test.
5- Introduction of techniques to detect B. hominis such as molecular methods.
6- Public preventive strategies should be carried out to decrease the risk of B. hominis infection by public education campaigns and through social media.
7- To study the causative agent associated with B. hominis occurance with colorectal cancer cases like reactive oxygen species (ROS).
8- Carrying out different activities could lower the risk for CRC.
9- Thee stop of eating processed meat while eating plenty of green leafy vegetables more frequently could lessen the risk of developing CRC.