Review for 10.1186/s12876-021-01841-2 (2021)

Reviewer’s report
Title: 
The prevalence of HEV among non-A-C hepatitis in Qatar and efficiency
of serological markers for the diagnosis of hepatitis E
Version: 
2 
Date: 
19 Apr 2021
Reviewer's report:
Thank you for the invitation to review the manuscript "The prevalence of HEV
among non-A-C hepatitis in Qatar and efficiency of serological markers for the
diagnosis of hepatitis E". In this study, the authors tested the frequency of HEV
in immigrants in Qatar and compared different assays (including serology,
antigen testing and PCR). 
Overall, this is a nicely written paper dealing with an interesting topic.
However, I have some comments and concerns:
1. It would if great interest to know which HEV genotype was prevalent. In
particular regarding the already raised question "What are the dominant routes of
infection …?" assessing the HEV genotype would be important. 
The HEV genotypes 1 and 2 are prevalent in the highly endemic areas such as
India, Bangladesh or Pakistan - where majority of immigrants in Quatar come
from. In contrast, HEV genotypes 3 and 4, which are zoonotic diseases,
primarily infect swine, and are prevalent in Japan and Europe as well as the U.S.
As mentioned, Qatar is a muslim country and pork is generally not consumed.
However, in immigrants it could be different, and swine meat consumption could
play a potential role in HEV infection.
2. Can authors clarify for how long immigrants have been in Quatar prior to
testing? And was there a difference regarding the anti HEV prevalence between
the countries of origin?
3. For better readability, could authors report viral loads as copes per ml or IE
per ml ? (This can be calculated from the CT values)
4. Could authors show a control group of people originating from Quatar. To
assess and possibly show the difference of anti HEV seroprevalence among
between workers from other countries and people from Quatar.
5. In the whole manuscript regarding ALT values (and other metric data): If you
show the mean (please show SD in brackets). If the variable is not normally
distributed, you need to show the median (and give interquartile range in
brackets).
Minor comments:
>In line 50 authors write: "Pigs serve as an important reservoir for HEV, and
exposure to pigs either by consumption of undercooked meat or through
contaminated water, especially after flooding, are the major source of infection
either in Europe or in Asian countries, respectively." Consumption of infected
meat (pork) and contaminated drinking water after flooding and reduced
hygienic conditions are 2 different pathways of infection - and also related to
different genotypes. Genotype 3 and 4 are zoonotic, whereas genotype 1 and 2
are associated with contaminated water. This should not be mixed and needs to
be stated more clearly!
>Line 68: Therefore, in this study, we aimed to study investigate the prevalence
of HEV virus among non-A-C hepatitis in Qatar. … delete the word "virus" …
directly after HEV …
>Line 96: "Authors write random samples" … Can authors secure that all of
these samples belong to workers from foreign countries - or is this mainly an
assumption?
>Line 169: "RT-PCR testing is considered the gold standard test for the
diagnosis of acute HEV (11, 15)."  This should be weakened … as in
immunocompromised patients, PCR indeed is the Gold standard. but in
immunocompetent individuals both, serology and PCR testing are feasible
options. The European Association of the Study of the Liver (EASL)
recommends the combination of serology and PCR to diagnose HEV infection.
> Line 212: "The overall percent agreement …" What is the "overall percent
agreement " … ? Please explain what this expression means … 
The current
phrasing is very difficult to understand for the reader … ?
>Discussion / Line 309: The intro / first sentence of the discussion should be
adapted. In my opinion it is not the fact that "identification of serological
markers remains a challenge" as stated by the authors. For sure, the variability of
different anti HEV assays does not facilitate HEV diagnosis. However, there are
established und widely accepted testing procedures, such as serology in
immunocompenten individuals, PCR in immunosuppressed patients, and if
possible, to combine both. The value of the HEV antigen tests remains less clear
- however, antigen testing may be used - and more data is needed. here it could
be mentioned that the EASL recommends combination of serology and PCR
testing (check if other big societies (e.g. AASLD) recommend the same approach
>Conclusion:- To start the conclusion with "HEV detection is largely ambiguous
since there are no well-established diagnostic standards." is quite difficult, as this
is not the reality. There good and established diagnostic standards, as already
mentioned above (see EASL guidelines, AASLD guidelines etc). Indeed there is
large variation inbetween diffrernt serological assays. in particular regarding
commercially available assays and inhouse assays. Therefore PCR testing
(possibly in combination with serology) is the best way … 
Table 
2.: - Patients / samples number 46, 66 or 68: had ALT levels of 15, 40 or
42. Were these cases considered as acute hepatitis E(?) If so, this should be
reassessed again. Isn't it the fact that these were more likely patients with
asymptomatic HEV infection(?)
Please give the range of normal of ALT values of your lab. But for sure, ALT of
15 IU/L is not an acute hepatitis!
Table 4:- please explain to the reader what means "overall agreement"
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
Yes
Are the methods sufficiently described to allow the study to be repeated?
Yes
Is the use of statistics and treatment of uncertainties appropriate?
Yes
Is the presentation of the work clear?
Yes
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes