Internal Medicine Topic Review: Insect Anaphylaxis
A long-term study of patients with stinging insect anaphylaxis
Stinging insect hypersensitivity reactions, including stings from yellow jackets, honeybees, paper wasps, hornets, and fire ants, are one of the most common causes of anaphylaxis. Life-threatening reactions occur in 0.8% of children and 3% of adults.
However, prompt treatment and proper referral of these patients to an allergist is important, because venom immunotherapy can completely eliminate the occurrence of future reactions and potential fatalities in a vast majority of patients.
People who have life-threatening reactions after insect stings often present to EDs because of the severity of their reactions. Unfortunately, our knowledge about the follow-up care received by patients after stinging insect anaphylaxis is limited. Thus, I want to review this study (http://www.ncbi.nlm.nih.gov/pubmed/23987196) to better understand the characteristics and subsequent treatment decisions that are made on these patients.
The senior author of this study was Dr. Carlos Camargo at MGH, who is well-known for conducting ER studies characterizing a multitude of patients, with investigators from Brown and Cornell. They analyzed 8 years of data, between 2001 and 2009, from the Thomson Reuters MarketScan Commercial and Medicare Supplemental Databases. This database includes 43 million privately insured individuals enrolled in 100 different health plans, including individuals 65 and older with Medicare.
They then used ICD-9 codes to identify patients with both anaphylactic shock and venom-specific diagnoses and created something called the Index Event, which was the stinging event that brought the patient to the ER. Afterwards, they used statistical software to analyze demographic and medical data one year prior to the index event, the index event itself, and 1 year after the index event, to create a story for these patients of what occurred before, during, and after the event.
Of the 43 million patients in the database, they identified 954 who had a stinging insect anaphylaxis. Prior to the index event, only 6% had asthma and 7% had allergic rhinitis. 3% had at least 1 allergist visit in the preceding year, suggesting a low prevalence of atopy in this population. Interestingly, only 1 patient had a comorbid diagnosis of mastocytosis, although the study was unable to capture whether additional patients were diagnosed with mastocytosis after the index event.
During the event in the ED, cardiorespiratory failure occurred in 7% of patients. Only 6% of patients were treated with epinephrine. Moreover, over 85% were treated and discharged from the ED. The remaining 15% were hospitalized, with a median length of stay of 1 day, with half of the hospitalized patients spending some time in the ICU. Importantly, no deaths occurred from stinging insect anaphylaxis. However, half of repeat ER visits occurred within 1 day, suggesting incomplete resolution of symptoms or a relapse from a biphasic reaction.
Post-discharge is where the results get interesting. Within 1 year after discharge, 69% of patients with stinging insect anaphylaxis filled at least one epipen autoinjector. That left close to 1/3 of patients without an EpiPen in this population. Even more galling (and I may be biased), but only 14% of patients with stinging insect anaphylaxis visited an allergist in the one year after the index event. For children, the rate was higher at 20%. The reason this is abominable is because many of these patients are candidates for venom immunotherapy, which is a life-saving intervention.
Dr. Feng is a content contributor to Knowmedge. You can see all his other posts on Knowmedge here, including his highly popular posts about Prepping for the ABIM Internal Medicine Board Exam.