Review for 10.1186/1471-230X-10-43 (2010)

Reviewer's report
Title:Severity of acute hepatitis and its outcome in patients with dengue fever in
a tertiary care hospital Karachi, Pakistan (South Asia):
Version: 3Date:5 January 2010
Reviewer: Dorothea Nitsch
Reviewer's report:
The authors have answered most of my questions to satisfaction. There are a
few queries with regards to the display of data which need to be addressed.
Major Compulsory Revisions
-The authors should mention under study design at start that they conducted a
cohort study of all dengue patients admitted to their hospital who were uniformly
tested on day of admission according to a standardised in hospital protocol.
Adding this at the end does not give enough emphasis to this very important
feature of this study.
-They should mention how many patients of all dengue admissions were
excluded due to pre-existing liver problems. If that was 50% then the cohort that
was analysed is not representative of all dengue patients but only those who did
not have pre-existing liver disease. I presume that alcohol consumption and
Hepatitis C is fairly low, but I don't know enough about the local setting, the
authors need to clarify this for the reader.
-Some analyses excluded those with no liver problems, i.e. those with no ALT
elevations. I don't think this exclusion is necessary, the authors could compare
those without ALT increase to those with mild/moderate and those with severe
ALT elevations.
-All the mortality analyses are biased by the fact that length of follow-up differed
between groups. Hence, authors have used Cox-regression for mortality
analyses, which is correct. However, figure 1, and table 1 are misleading as
proportions do just take totals at the end which is not allowing for the difference
in length of follow-up.
In line with the analytic strategy of the authors they should also show their crude
data accordingly: Figure 1 should be a Kaplan-Meier plot of survival (or mortality,
whatever the authors prefer) over time (days of stay), with numbers at risk in
each group displayed below the graph. Ideally one would see 3 lines - those
without ALT elevations, those with mild/moderate and those with severe
increases. Here a log-rank test should be used.
-Table 1 must have some errors in terms of copying the numbers from the output.
I don't understand how the percentages and the numbers work out- the column
heading for mortality indicates that % is in the bracket and numbers of people is
given in front, but it is the other way round in the table. Also, how are 3 out of 81
people with severe hepatitis and dengue fever only 0.6%? Or why are 9 out of 22
people (bottom row) only having a mortality of 10.8%? This is possible, if
mortality is an incidence rate (so number over person-time), but then it would be
necessary to relabel the column accordingly, and also give confidence intervals.
P-values in this table should be consistently displayed. '<0.00' is incorrect.
-Figure 2 should add a measure of uncertainty to the bars, perhaps a box-plot
would be better.
-Table 2 should add total numbers and all p-values should use Fisher's exact
tests to be on the safe side.
Level of interest: An article of importance in its field
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 declare that I have no competing interests.