Comments on: HPV Clearance in a journal article

Question: HPV Clearance in a journal article

zeek321 — Mon, 25 Feb 2008 18:45:30 -0800

Clearing HPV: Help me understand this journal article, specifically the concept of rate ratio and how it translates into real-world risk.

Let's say someone is found to be carrying the hpv-16 strain. Based on this article, what's the chance that they will test negative viral DNA in X number of months? What's a rate ratio?

Can anyone recommend more/better articles on clearance statistics? I'm most interested in the high-risk strains. Here are some more snippets I found that I haven't carefully examined yet.

The question underlying all of this, of course, is if a guy or gal is infected with a high-risk strain, what are the chances that it'll be completely gone in a X number of months with Y confidence?

By: drpynchon

drpynchon — Mon, 25 Feb 2008 19:04:11 -0800

The rate ratio is comparing the clearance rate in people for the higher-risk strains to those with lower-risk strains. In other words, when it says that the rate ratio for HPV-16 was 0.47, what that means is that patients with HPV-16 were 53% less likely to clear the virus than the comparison low-risk strains. In other words, it's harder to clear than the other strains.

From the abstract, it's impossible to know what the absolute clearance rate is or for that matter what the time course or mean time to clearance was.

By: drpynchon

drpynchon — Mon, 25 Feb 2008 19:19:15 -0800

Here's another paper with some more data that might be of interest to you. They quote the median and mean retention time as 19.4 (11.4–27.5) & 18.3 (12.9–23.7) months with 95% confidence intervals as noted. 62% of people were still infected at 1 year with a 95% confidence interval of 46–78%. I didn't read the paper thoroughly enough to tell how reliable those numbers may or may not be though.

By: googly

googly — Tue, 26 Feb 2008 09:29:24 -0800

Based on a very brief skimming of the article:

What's the chance that they will test negative viral DNA in X number of months?

"Globally, 23 percent of HPV infections were still present at 1 year and 7 percent at 5 years. Clearance rates were lower for HPV 16 than for low-risk HPV types."

Their data indicates that HPV-16 clearance rates were lower (e.g., it persisted longer) than any other strain. Their analysis does not allow us to draw specific conclusions for clearance rates by month, in part because the time interval between testing was 6-9 months. That is why their graph (Figure 1) has stair-steps rather than curves. However, from this figure, it appears that the chances of still having HPV 16 dropped to ~40% after 6 months, and then to ~30% after ~20 months, and stayed at that level for the next 3 years.

What's a rate ratio?

drpynchon gives a good definition above. A rate ratio is simply the result of dividing the rate in one population by the rate in another.

If a guy or gal is infected with a high-risk strain, what are the chances that it'll be completely gone in a X number of months with Y confidence?

This cannot be definitively determined from the study you cite, because:

(1) It only looks at women, in a small Columbian sample.

(2) It does not calculate clearance rates month-by-month.

(3) It indicates that the clearance rate depends in part upon patient characteristics, including age, type of HPV infection, and oral contraceptive use.