potential issue with lineage typing

[rderelle]

Dear Jody,

I came across some strange results for a SRA sample (ERR4797559) which is supposed to be part of the lineage 1.2.2 according to the tb-profiler website and confirmed with a local installation of tb-profiler.

However, looking at the mutation profile of this sample, I found 9 out of the 10 snp barcodes for lineage 1.2.2.2 to be present and I did not understand why this sample wasn't labelled '1.2.2.2'.

I then had a look at the python code and I believe I found the issue (function 'barcode' of the file barcode.py; line 70):

    for l in barcode_support:
        # If stdev of fraction across all barcoding positions > 0.15
        # Only look at positions with >5 reads
        tmp_allelic_dp = [x[1]/(x[0]+x[1]) for x in barcode_support[l] if sum(x)>5]
        if len(tmp_allelic_dp)==0: continue
        if stdev(tmp_allelic_dp)>0.15: continue

In my case, the fractions for the lineage 1.2.2.2 snps (tmp_allelic_dp) are [1.0, 0.0, 1.0, 1.0, 0.9622641509433962, 1.0, 1.0, 1.0, 1.0, 0.9666666666666667] and the linage is being discarded because the standard deviation is above 0.15.

If my findings are correct, I'm wondering wether this threshold makes sense since it discards lineages with 9/10 of barcode snps found. May I ask what is the rational behind this threshold?

Also, I found this problem to be present in about 6% of all SRA samples I have tested (>2k samples).

Thanks and hope this helps! Romain

ps: I could share with you the BAM file generated by tb-profiler for this particular sample.