Lyme Disease 2018: CDC Report On Insect-Borne Disease Inflates Zika's Role

The U.S. Centers for Disease Control and Prevention’s Vital Signs report released on May 1 showed that the annual number of illnesses spread by mosquitoes, fleas, and ticks tripled from 2004 to 2016. This may sound like an alarming increase, but the CDC didn’t seem to give us the whole story, leaving out key details about the impact of climate change and unusual disease-related events in recent years.

In the teleconference accompanying the release, the CDC chalked up the uptick in illness to an increase in overseas travel and trade, which has brought diseases like chikungunya and Zika to the U.S. since 2004. What it didn’t do was attribute the increase in illnesses to climate change in any meaningful way, only going so far as to mention that as the climate warms, the range of disease-carrying insects expands, and the length of time they’re active each year increases. Furthermore, while the CDC report shows that the number of confirmed cases in 2016 was indeed triple the 2004 number, it’s important to note that the increase wasn’t a steady one. Looking at the CDC’s numbers, it seems pretty obvious that 2016 was actually an outlier.

The graph above shows the CDC’s numbers for confirmed cases of 16 different bug-borne diseases, including Zika virus, Lyme disease, babesiosis, and West Nile virus. The total number of diseases more than tripled from 2004 to 2016, but this graph makes it very clear that the trend was not linear. In fact, as Ars Technica pointed out on May 2, 61 percent of the increase from 2004 to 2016 — 41,680 cases — was due to Zika cases in 2016 alone. Anyone who’s been paying attention to the news over the past two years should recall that cases of Zika virus, which wasn’t well characterized in the U.S. before then, suddenly spiked in 2016 in South America, spreading northward.

Significantly, most of the 41,680 Zika cases mentioned in the new CDC report occurred in U.S. territories (Puerto Rico, the U.S. Virgin Islands, and American Samoa), and only 5,168 were in U.S. states. Of these, almost all of them were travel-related, suggesting that Zika isn’t really on the rise as an endemic disease in the continental U.S. This point isn’t meant to downplay the significance and concern of Zika in these U.S. territories, only to show how the CDC has failed to present this information in a way that’s relevant and meaningful for most people in the U.S.

Besides this Zika outlier, the CDC data do show an increasing number of vector-borne diseases, most of which can be attributed to increasing numbers of Lyme disease cases. Unfortunately, as Ars Technica also points out, part of this is due to changes in CDC reporting that occurred in 2008, which means that even suspected cases now count as confirmed cases.

So what do all these numbers mean for you? They mean that you still should wear insect repellant and check yourself for ticks after a walk in the woods. What they don’t mean is that we’re in the midst of an insect apocalypse. So chill and enjoy the outdoors.