Screening for colorectal cancer using the faecal occult blood test: a critical literature review

Diarrhoeal pathogens in the stools of children living with HIV in Ibadan, Nigeria

Introduction

Diarrhoea can be debilitating in young children. Few aetiological investigations in Africans living with human immunodeficiency virus (HIV) have been performed since antiretrovirals became widely available.

Methods

Stool specimens from children with diarrhoea living with HIV, and HIV-uninfected controls, recruited at two hospitals in Ibadan, Nigeria, were screened for parasites and occult blood, and cultured for bacteria. Following biochemical identification of at least five colonies per specimen, diarrhoeagenic Escherichia coli and Salmonella were confirmed by PCR. Data were line-listed and comparisons were made using Fisher's Exact test.

Results

Only 10 children living with HIV could be enrolled during the 25-month study period and 55 HIV-uninfected children with diarrhoea were included for comparison. The most common pathogens overall were enteroaggregative E. coli (18/65, 27.7%), enteroinvasive E. coli (10/65, 15.4%), Cryptosporidium parvum (8/65, 12.3%) and Cyclospora cayetanensis (7/65, 10.8%). At least one pathogen was detected from seven of ten children living with HIV and 27 (49.1%) HIV-uninfected children. Parasite detection was associated with HIV positive status (p=0.03) with C. parvum specifically recovered more commonly from children living with HIV (p=0.01). Bacterial-parasite pathogen combinations were detected in specimens from four of ten children living with HIV but only 3(5.5%) HIV-uninfected children (p=0.009). Stools from five of ten children living with HIV and 7(12.7%) HIV-negative children (p = 0.014) contained occult blood.

Discussion

Even though children living with HIV present infrequently to Ibadan health facilities with diarrhoea, their greater propensity for mixed and potentially invasive infections justifies prioritizing laboratory diagnosis of their stools.

Faecal Occult Blood Point-of-Care Tests

Background

Early detection of colorectal cancer decreases the risk of mortality. Faecal occult blood tests (FOBT) are recognised as a useful tool for colorectal cancer screening. These non-invasive, rapid, and easy-to-carry assays are very often used as a point-of-care test and for self-testing. On the market, there are various types of FOB tests available, including chemical and immunochromatographic tests, which are based on different detection methods and differ in their sensitivity and specificity.

Conclusions

Clinicians should be aware of the causes of false-negative and false-positive test results, which can vary depending on the test. Additionally, stool sampling bias may be a source of error and must be considered by the clinician. The current FOBT methods are subject to various interfering factors; items such as proper preparation of the patient prior to testing or the clinician’s knowledge of testing limitations are key in correct interpreting results. Novel technologies such as FOBT DNA tests, micro RNA tests, and biochips equipped with bacteria can indicate bleeding from the gastrointestinal tract and improve diagnostics process.

An Overview of Colorectal Cancer Screening

Colorectal cancer ranks highly amongst all cancer sites in incidence and contributes to a substantial number of cancer related deaths in the United Kingdom. However, screening of average risk individuals has been shown to reduce both disease associated mortality and incidence. This paper provides an overview of both current and future screening methods for colorectal cancer, as well as current practice for screening in both average and high risk individuals.