Review for 10.1186/1471-230X-12-122 (2012)

Reviewer's report
Title:Blastocystis spp. incidence in patients with gastrointestinal symptoms: a
case-control study
Version: 2Date:9 April 2012
Reviewer: Chad Porter
Reviewer's report:
The authors report on the prevalence of Blastocystis spp. among a population of
patients with a variety of gastrointestinal conditions such as inflammatory bowel
disease (IBD) and irritable bowel syndrome (IBS). Compared to a reference
population without gastrointestinal symptoms or disease, the prevalence of
Blastocystis spp.was slightly higher in those with gastrointestinal conditions;
however, the magnitude of this difference appeared to be disease specific. While
interesting, there are some specific issues that need to be addressed before
manuscript is suitable for publication. Below I have outlined a few major concerns
as well as some minor points that should be addressed.
Major compulsory revisions:
1. There is no attempt to describe the temporality of the findings. It is unclear if
the apparent increase in Blastocystis spp. prevalence among patients with
gastrointestinal conditions compared to a reference population occurred prior or
subsequent to the onset of the chronic disease. This seems to be a significant
limitation in the findings. This is highlighted in the proposed title which states
“Blastocystis spp. incidence…”; the authors provide no measure of incidence
throughout the paper making the title quite misleading.
2. Statistical analysis; the authors report simple proportions and compare
multiple chronic disease populations to the reference population. However, there
is no apparent attempt at alpha-adjustment to control for multiple comparisons to
the reference population across the chronic disease states. Additionally, the
authors should include 95% confidence intervals for the prevalence parameter
estimates. The authors inconsistently report p-values; where less than 0.05, they
are frequently reported to the 4th digit. However, “non-signficant” differences are
reported as “>0.05”. Additionally, there is no attempt to adjust for potential
confounders or assess for effect modification associated with other potentially
important covariates.
3. There is no traditional ‘Table 1’ to allow the reviewer to compare the study
populations in terms of race, ethnicity, primary complaint (among the chronic GI
disease population). The authors state there were no differences between the
study populations in terms of gender or age. Ages are reported with what appear
to be standard deviations or standard errors. From the manuscript, it is unclear
what statistical comparisons were made to state that “there was no statistically
significant difference between groups.” A complete ‘Table 1’ would remove
significant concerns regarding potential socio-demographic differences across
study populations.
4. The authors reference a table [Table 2] that appears to have been excluded
from the submitted version of the manuscript.
5. Bacterial causes of infectious gastroenteritis (namely Campylobacter and
Salmonella) have been repeatedly linked to IBS and IBD; however, there is no
mention of these antecedent infections. It is unclear if the researchers assessed
for these infections either through a medical chart review or questionnaire. At a
minimum this should be a discussion point and the impact that this important
potential confounder may have on the observed results should be described.
Minor essential revisions:
1. In the first sentence of the abstract, the authors refer to Blastocystis spp. as a
bowel disease; however, the literature is mixed on whether Blastocystis spp. is a
pathogen – it is clearly not a “bowel disease.”
2. There are numerous grammatical and punctuation errors that should be
corrected (eg, use of commas instead of periods, incorrect word choice, etc).
3. There are several sections of the discussion that could use some additional
references.
4. The authors should expand the discussion to include details on potential
pathological mechanisms of the observed associations.
Level of interest: An article of limited interest
Quality of written English: Needs some language corrections before being
published
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I have no competing interest.