DEAR DR. ROACH: I recently had a bout with norovirus and have been reading about this class of viruses. They seem like perfect vehicles for infecting millions of people. What I keep reading is that they are seemingly self-limited, usually lasting three days or so. So, my question is, what exactly makes them self-limited? They seem so invincible. What is it that stops their effect on the body after a few days? Also, is the answer to this question something that is currently being studied by researchers as a potential treatment? (I am hoping that the answer isn’t that their human host wouldn’t survive after too many days of infection.) — S.
ANSWER: Noroviruses, and their close cousins, are highly infectious viruses that can cause nausea, vomiting, abdominal pain and diarrhea. The incubation period from exposure to symptoms is short — one to two days. It’s estimated there are 20 million cases a year just in the U.S. The virus is resistant to cleaning, some disinfectants and heat.
People with normal immune systems usually recover in about three days, but may continue to be infectious for weeks. It’s our immune responses, both humoral (B cells, which make antibodies) and cellular (T cells), that combine to control the infection and provide pretty good long-lasting immunity — but only to that specific strain, of which there are dozens. Unfortunately, a person can still get repeated infections from different viral strains. Fortunately, death from norovirus is rare (less than one person per 100,000) and usually in people who are so frail that the fluid loss causes organ failure.
There are no specific treatments for norovirus, and the most important treatment is making sure a person gets adequate fluid and salt replacement. Since immunity is what stops norovirus, future directions may include development of a norovirus vaccine.
DEAR DR. ROACH: I read your recent column about the MESA calculator. I found the test myself and input my numbers. But I found that I have a higher 10-year risk when I state that I am using a statin; each time I omit the statin risk, however, my score is actually lower. Common sense tells me that the 10-year risk number would be lower while using a statin. Comments? — G.L.D.
ANSWER: Statins do reduce the risk of developing heart disease, but the benefit is mostly for people with the highest risk. You got a paradoxical answer because you didn’t change your cholesterol numbers. If you had put in the cholesterol results you had before starting the statin (telling the calculator you took no statin), and then compared it with the new cholesterol results on the statin (checking off the box that you are now taking it), you would have seen a reduction in your risk.
A person who begins taking a statin and gets favorable cholesterol results doesn’t have the same risk as a person who has had those same good levels for many years without a statin. You would see the same result with blood pressure in many of the calculators.
There remains controversy, but most data suggests that, eventually, with improved cholesterol or blood pressure for years, a person’s risk eventually becomes almost the same as if they had those numbers without treatment. Not every cardiac risk calculator adjusts based on whether you are on treatment, but a few calculators are able to adjust your risk for the amount of time you have been on treatment.
Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.
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