Crash Course – Epidemiology

this is how I feel when someone coughs without covering their mouth

this is how I feel when someone coughs without covering their mouth

Alright party people, let’s get right down to it. The Ebola outbreak is on everyone’s mind right now and I felt obligated as your friend and favorite science blogger (let me have my dream) to clear up a few key concepts that get tossed out by the media like candy wrappers. Epidemiologists (scientists who study disease) have their own technical lingo when it comes to disease and GOSH DARNIT I want you to know it too. Hey, look at me…I care.

The terms of the trade…

Agent – the thing that causes the disease, or put another way, the element that is always present with the onset of the disease and whose presence is essential for the disease to occur.

Reservoir – the habitat where the infectious agent lives and thrives. This can be a stagnant, jungle pond or the intestinal tract of a human being

Carrier – person or critter (bat, monkey, bird) that can harbor the infectious agent and is capable of giving it to others. The carrier often lacks any signs or symptoms of having the disease.

Host – Any living thing that can be infected by a disease causing agent under normal conditions. If it’s a brisk November morning and you’re reading “Horton Hears a Who” to a small room of kindergartners on the carpet and half of them have the sniffles, then you are the perfect host for the Rhinovirus (cold). All the conditions are perfect.

Vector – living intermediary between a reservoir and a host. Mosquitoes are classic vectors, especially since they’ll suck blood from a variety of victims. They are equal opportunity pains in the butt.

Transmission – the mode or mechanism by which the disease causing agent is spread (air, water, food, person to person contact, contact with object)

Virulence – refers to the infectious agent’s ability to cause disease. I think of it as a measure of potency. On the other hand, infectivity describes that pathogen’s ability to spread disease to other hosts. When Chicken Pox shows up at a party it doesn’t just stand in the corner by itself. It turns the music up, heads to the center of the floor, and tries to dance with everybody.

Zoonoses – infectious diseases that are transmissible from animals to humans.
It’s funny just how foreign this term is for many of us, since there are so many devastating diseases to the human population (Avian flu, Swine Flu, Black Plague, Rabies, Lyme’s) that we acquire from other species.

Morbidity – is essentially an assessment of just how sick the disease in question makes you. It also has a statistical value representing the relative occurrence of disease in a population.
The definition of morbidity has a wonderfully legal sound to it, but the further a disease moves you away from your normal, healthy physical or mental state the higher the morbidity of that disease is. It is the degree of transformation your body goes through in the course of a disease.

Let’s put it all together…

Gina flew in yesterday from Boston on a late flight back to Georgia. The 5 year old behind her showed her all of his limited edition Shrek action figures on the ride back. One of them was sticky from the gummy worms he’d eaten earlier. She’d gotten back at 10pm but her college peeps were in town and the beers at Karma Mike’s Grill were still half priced until midnight. Work came way too early that next day. She only slept 3 hours and the AC in her office was at full blast.
By noon the sneezes started and her nose would not stop running. Around 2:30 all the name brand, instant coffee in the world could not keep her eyes open to read through all her emails. Later that night her throat felt scratchy and her muscles ached as if she’d lost a cage match. That’s when she remembered the kid on the plane and the suspiciously sticky Shrek. Suddenly Gina understood everything that was happening to her.

Our Cast…

Gina – Host

5 year old – Asymptomatic carrier

Shrek action figure – mode of indirect transmission

Respiratory tract – reservoir of virus

Rhinovirus – infectious agent

I hope this helps. Stay curious, stay classy, and never stop learning my friends 🙂

That Carpal Tunnel Thing…

Body parts are like politicians. You don’t really think about what they do until something goes wrong. Consider the median nerve. “What’s that?” Well it’s only the peripheral nerve responsible for sensation and motor control of the fingers within the palms of each hand (except for the little finger, but pinkies have problems with authority).

"You say it your way and I shall say it mine."

“You say it your way and I shall say it mine.”

Don’t feel bad if you’re not facebook friends with the median nerve. It never really hits the news until it gets squeezed. Yes, squeezed. Everyone has heard of Carpal Tunnel syndrome, Carpal Tunnel, or “Copper tunnah” if you were raised in the land of sweet tea and magnolias.

The carpal tunnel is a narrow channel of ligaments and bone in the wrist that the median nerve passes through like the DC metro train. In carpal tunnel syndrome this space begins to narrow, compressing the median nerve which leads to numbness and chronic pain in the hand, fingers, and wrist.

What causes the squeeze?


I really wanted to give this diagram a high five just now. Weird, I know.

Did I mention that the carpal tunnel is narrow? No space is wasted in the body and the median nerve isn’t just floating happily in first class with all the leg room in the world. It is literally surrounded on all sides by 9 flexor tendons, vessels, small muscles, and of course, the carpal bones of the hand. In such a tight space if any one of those tendons decides to swell (and you know how tendons can get) the median nerve will get squeezed tighter than a dachshund wrestling a Saint Bernard for a bean bag chair.

I’ll just give you a moment to absorb that imagery…

Risk Factors

“Risk” is just a sly statistical term to describe how much wiggle room an individual has in avoiding a disease or condition. In this case, risk factors include any condition that could significantly alter the space within the carpal tunnel.

Injury – wrist fractures, and dislocation of the carpal bones of the wrist

Chronic Illness – Diabetics or anyone with an increased risk of nerve damage, Impaired kidney function, obesity, prolonged fluid retention during pregnancy, or persistent inflammatory conditions

and then there are the Statistically cursed…


“Why did I play World of Warcraft for 7 hours Yesterday?”

Statistically women are 3 times more likely than men to develop CTS, possibly due to their smaller carpal tunnels. Of course, those women who do develop CTS could have any combination of the risk factors that I mentioned above. So I wouldn’t go out making predictions at the bar with your tape measure just yet. A perfectly healthy woman or man with no signs of CTS could have smaller wrists than a woman with CTS.

Work Related? – There are a lot of people (including myself) who associate CTS with mind-numbingly repetitive tasks, such as typing or assembly line work. We can’t start pointing the finger at any one profession (and I know you want to). We can’t just say, for example, that packaging chicken parts for Tyson causes carpal tunnel syndrome. However, it has been established that CTS is three times more common among assembly line workers than individuals who perform data entry.

Any prolonged activity that puts stress on the wrist could easily exacerbate an underlying condition that could lead to CTS. Even if you have wrists the size of tree trunks I wouldn’t compete in any 3 day, speed origami marathons until all the facts are in.

Stay classy, stay curious, and never stop learning my friends 🙂