Topics in Allergy
Allergy To Stinging Insects-Sometimes Clear But There Are Grey Zones & Difficult Decisions:
In most patients decisions regarding immunotherapy (allergy shots) for stinging insect allergy are straight forward.
If an adult has had a systemic reaction to a sting (hives, breathing problems, low blood pressure) or if a child has had a systemic reaction that involved more than a skin reaction, THE RISK OF SIGNIFICANT SYSTEMIC REACTION WITH EACH FUTURE STING IS 55-65%. ALLERGY SHOTS TO THE VENOMS WILL REDUCE THE RISK OF REACTION TO 1-2% CHANCE OF REACTION WITH EACH STING.
WHEN ALLERGY SHOTS ARE STOPPED (AFTER 5 YEARS) THE RISK OF REACTION RISES TO ABOUT 8% WITH EACH STING AND REMAINS AT THIS LEVEL.
UNFORTUNATELY THERE ARE MANY GREY AREAS WHERE OTHER CONSIDERATIONS APPLY. MOST OF THESE MORE DIFFUCULT DECISIONS ARE LISTED BELOW:
1. ADULTS WHO HAD MILD SYSTEMIC REACTIONS. Most adults with mild systemic reactions experience similar reactions with subsequent stings. It is unusual, though certainly possible, for future stings to be significantly worse. Currently immunotherapy (allergy shots) is recommended for all adults who have had any systemic reaction, even if it was mild.
2. CHILDREN WHO HAD ONLY HIVES TO PRIOR STING without any other symptoms of systemic reaction. 90% of children who experienced only hives to a prior sting will have no reaction to future stings even without treatment. 10% will have a similar hive reaction to future stings. One patient out of 180 had a severe reaction to a future sting. The risk of worrisome reaction is, therefore, very low but not zero. Currently allergy shots are not routinely recommended in this situation but could be considered in some circumstances. Similarly, you must weigh this information when making a decision about carrying adrenalin.
3. PATIENTS WHO REACTED TO A SINGLE INSECT STING BUT SHOW POSITIVE TEST RESULTS TO SEVERAL VENOMS. A decision must be made to desensitize with only one venom or more than one venom. There are advantages and disadvantages to either decision.
4. PATIENTS WHO HAD A LARGE LOCAL REACTION TO A STING BUT NO SYSTEMIC REACTION. Current recommendations are to not routinely test people in this category. 80% of patients who had large local reactions to a sting will have positive allergy tests. 3% of children with large local reactions and 14% of adults with large local reactions will have a systemic reaction to future stings. Most of the patients who later had systemic reactions had originally had large local immediate reactions rather than large local delayed reactions. Currently allergy shots are not recommended for patients with large local reactions but allergy shots clearly reduce the severity of large local reactions and nearly eliminate the risk of systemic reactions. They could be considered in some circumstances.
5. PATIENTS WITH HONEYBEE ALLERGY. Patients with reactions to honeybee stings that are not treated have a higher recurrence rate with future stings. Unfortunately they also have a higher incidence of reactions to allergy shots than those getting shots for other venoms. Allergy shots for honeybees are slightly less effective than allergy shots for other venoms (honeybee shots reduce risk of reaction to future stings to about 10% while shots to other venoms reduce risk to about 2%). When allergy shots to honeybees are stopped the risk of reaction to future stings increases more than when shots to other venoms are stopped. Some recommend not stopping allergy shots to honeybee venom because of this.
6. PATIENTS WHO REACTED TO A STING BUT SHOW NO REACTION ON SKIN TESTS. A few patients with no reaction to skin tests will show allergic sensitivity on a blood test for venoms (RAST). A few will show sensitivity if the skin tests are repeated 6 weeks later. If you have reacted to a sting and have negative skin tests, a RAST test for venoms should be done. If this is negative the skin tests should be repeated in 6 weeks.
Some patients who have had a reaction to a sting will not show evidence of allergy even with repeat skin tests and the RAST test. Some patients in this situation have still had serious systemic reactions to future stings. These reactions occur through mechanisms other than true allergic mechanisms and are not helped by allergy shots. Adrenalin should still be carried to treat reactions and patients should still avoid taking beta blocker or ACE inhibitor medications.
7. HOW LONG SHOULD WE CONTINUE ALLERGY SHOTS FOR VENOMS BEFORE STOPPING? Current recommendations are to continue allergy shots for 5 years and then stop. However:
Patients with very severe reactions to stings (respiratory or cardiac arrest or severe shock) have higher recurrence rates of reactions to stings and more severe reactions to stings than other patients when allergy shots are stopped. Some recommend continuing allergy shots indefinitely in this group.
Patients with honeybee sting reactions are in a similar situation (see above).
Patients who have many reactions to allergy shots have higher risk of sting reactions when shots are stopped and may want to consider staying on allergy shots indefinitely.
8. A decision to start allergy shots for stinging insect venoms must take into account:
a. The severity of the prior reaction.
b. The risk of future reactions.
c. The type of insect (see honeybees above).
d. Exposure to stinging insects.
e. Other health problems that might complicate treatment or complicate reactions to stinging insects.
9. Patients with reactions to stinging insects should also remember:
a. Common sense measures to avoid being stung. Sounds obvious but just as important as any other measures.
b. Importance of not taking beta blocker medications or ACE inhibitors.
c. Use of adrenalin and medic alert bracelet.