www.cdc.gov/mrsa
We are currently in peak tick season here in the Northeastern United States.
It might be hard for clinicians elsewhere to understand just how profoundly this changes our assessment of fevers and rashes. But consider this — ordering the trio of Lyme antibody, Anaplasma PCR, and Babesia PCR is as much a part of the routine diagnostic evaluation of the febrile adult in the summertime as ordering an influenza swab in the winter.
So it was with some amusement that I received the following email from a patient recently who had just been hiking in New Hampshire (some details changed as always for confidentiality reasons):
Hi Dr. Sax,
Just got back from a 2-night camping trip, and think I might have gotten a spider bite [emphasis mine] behind my left knee. There’s a dark area in the center, and a red rash spreading around it — no bull’s eye.
Anything I should do?
Gerry
He included in this email a photo of the rash, which was pretty classic for erythema migrans, the tell-tale rash of Lyme Disease.
In fact, everything about his story was consistent with Lyme, including the time of year, the recreational activity (remember, hike in the center of the trail, folks!), the location of the rash (popliteal fossa is a favorite site for tick bites), and even it’s appearance — many erythema migrans rashes lack central clearing. It’s a common misconception that all Lyme rashes must be have a “bull’s eye.”
But for today, let me just focus on one piece of Gerry’s clinical history that defies explanation:
I think I might have gotten a spider bite.
I’ve never understood this mass psychosis. We first noted it when community-acquired MRSA spiked in the early 2000s. A shockingly high proportion of people seeking attention for their boils, furuncles, and skin abscesses mistakenly attributed them to spider bites.
It got so bad that the CDC issued special graphics, suitable for framing, two of which grace this post.
“When in doubt — check it out.” Clever. While these graphics may lack some of the artful touches of wartime posters warning about sexually transmitted infections, they nonetheless have a blunt and direct appeal.
In reality, spider bites are quite rare:
Spiders tend to avoid people, and have no reason to bite humans because they aren’t bloodsuckers and don’t feed on humans … In North America, there are only two groups of spiders that are medically important: the widow group (which includes black widows) and the recluse group (brown recluses).
Entomologists say that spiders as a rule are fearful of humans — makes sense, we’re much bigger than they are! They only bite when surprised, or trapped.
Which leaves us with this mystery — why do our patients so often think they have a spider bite? It’s a mystery to me.
But perhaps you, smart readers of this ID blog, might have an idea?