Predicting the Risk of Subsequent Insect Stings


 
Carol Smith, MD checks a patient's medical history.

The majority of people who are stung by an insect for the first time do not have a life-threatening allergic reaction to the venom. However, the type of reaction you have to that initial sting may offer clues to how your body will react to subsequent stings.

The threat of an anaphylactic reaction is a concern to anyone who has been stung by an insect; however, fewer than five percent of the population will have a systemic reaction. The insects that cause the majority of life-threatening reactions in North America are honeybees, yellow jackets, yellow hornets, white-face hornets, paper wasps, and fire ants. Following the initial sting, most patients look to an allergists for management of future problems, says Carol Smith, MD, of Birmingham Allergy & Asthma Specialists, PC.

“Insect allergy is relatively easy to diagnose and treat, but it remains an enigma in many ways,” she says. “Predicting future sting reactions is important for preventive treatment and emergency management of affected patients.”

Most insect stings produce a local reaction that can cause redness and swelling at the site, and generally resolves without treatment. About five percent of people will report an abnormally large or prolonged swelling at the site of the sting (large local reaction). A systemic reaction and/or anaphylaxis occurs in one percent of children and three percent of adults.

“We use these symptoms to predict the effect of future stings, because people want to know their risk,” Smith says. “We don’t have a great lab test to accurately predict the outcome of a future sting. Remarkably, the single best predictor of the outcome of a future sting is still the history of reaction to a previous sting. It is important to integrate the detailed history of sting reaction with the statistical predictions of many factors and a knowledge of the natural history of the condition. Some decisions include when and whether to do any diagnostic tests, whether to prescribe an epinephrine injector, whether to start venom immunotherapy, and what to do about other risk factors such as medications and underlying conditions.”

How big is the risk? The general population risk of a sting being life-threatening is about two percent. The risk increases to about five percent for a person who has a large local reaction at the sting site. Systemic symptoms away from the sting, such as breathing difficulties or fainting, raises the risk to 20 to 60 percent, Smith says. Patients with anaphylaxis requiring emergency treatment have the highest risk of problems with a future sting.

It is important that these patients be referred to an allergist for evaluation and treatment to reduce the risk of severe problems should another sting occur. During the evaluation, the allergist will ask the patient questions about when and where he was stung, the severity of the reaction, medicines he is taking and exposure to the outdoors.

“If a person comes to me with a large local reaction only, we are less likely to recommend testing because the risk of a future problem is low,” Smith says. “If the patient had a severe systemic reaction, he is at moderate to high risk and we do skin testing to confirm an allergy. We test for all five flying insects and usually fire ants.”

If a risk is significant, Smith recommends immunotherapy to desensitize the patient to the venom. Therapy includes all venoms that are positive on skin testing and begins with a small dose that is increased according to a schedule. “These shots are continued for three to five years and are proven effective in preventing subsequent systemic reactions,” she says.

Smith says that effective emergency management of patients with insect stings is imperative to providing appropriate care for possible future incidents. “Current guidelines for sting anaphylaxis in the emergency room require that these patients be released with a prescription for an epinephrine auto-injector and a referral to an allergist/immunologist for subsequent diagnostic testing and treatment. Studies show that these guidelines aren’t being followed often,” she says.

“A market study followed 954 patients who had an ER visit for anaphylaxis. Of those patients, 85 percent were discharged directly from the ER. Half of the remaining patients were admitted to an ICU, and one-fourth of those had cardiorespiratory failure. 69 percent filled at least one prescription for epinephrine, and only 14 percent visited an allergist. Insufficiency of care and failure to visit an allergist places these patients at risk for further anaphylaxis,” Smith says. “The burden is not on the Emergency Department or a patient’s primary doctor to determine who is at risk, but they need to send the patient to an allergist who can make the decision.”

 

 

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