# Poor taxonomic classification of sputum samples

**URL:** https://forum.qiime2.org/t/poor-taxonomic-classification-of-sputum-samples/6320
**Category:** User Support
**Created:** [October 4, 2018, 12:37pm UTC](https://forum.qiime2.org/t/poor-taxonomic-classification-of-sputum-samples/6320 "2018-10-04T12:37:50Z")
**Posts on this page:** 1
**Showing post:** 10

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### Author: ![Nicholas\_Bokulich](https://forum.qiime2.org/user_avatar/forum.qiime2.org/nicholas_bokulich/32/19937_2.png) [@Nicholas\_Bokulich](https://forum.qiime2.org/u/Nicholas_Bokulich)
#### Post date: [October 5, 2018, 9:19pm UTC](https://forum.qiime2.org/t/poor-taxonomic-classification-of-sputum-samples/6320/10 "2018-10-05T21:19:38Z")

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Thank you for testing that.

If vsearch gives the same classifications, then read orientation is not the issue.

It also looks like you used full-length 16S as a reference for vsearch? (if you did, good — then trimming is not the issue either). If so, the pre-trained classifiers will not help either.

At this point I think the most likely possibilities are:

1. You have a large proportion of non-target DNA (e.g., host DNA)
2. There is something wrong with your query sequences (e.g., adapters or other non-biological DNA in the sequences).

Check out [this post](https://forum.qiime2.org/t/classify-consensus-vsearch-high-number-of-unassigned-features/2291/3), particularly the part about checking some of the unassigned sequences with NCBI blast... that will help figure out if you have some non-target DNA.

Let us know what you find!

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