What are Serum Sickness-Like Reactions?
Serum sickness is a range of symptoms that include skin rash, joint stiffness/pain, facial and extremity swelling, and fever. Sometimes vomiting or respiratory distress happens. It may be mistaken for anaphylaxis.
Serum sickness and serum sickness-like reactions (SSLRs) differ in what causes them. Antiserum, anti-venom and insect stings trigger a true serum sickness. Serum sickness-like reactions can look like classic serum sickness. They are typically less severe and happen following a reaction to a variety of medicines, vaccines and some infections.
What Causes a Serum Sickness-Like Reaction?
In a serum sickness-like reaction, the body’s immune system mistakenly identifies a substance (commonly an injectable medicine) as harmful. The result is an immune system response from the medication. It happens again if you give the same medication.
Although the clinical signs and symptoms for classic serum sickness and serum sickness-like reactions are the same, SSLRs do not have a reproduceable immune response.
For example, if a child takes amoxicillin for an ear infection and develops SSLR, the child can likely take amoxicillin again in the future without problems. In fact, many times the SSLR develops after the child is done taking the antibiotic. It may develop in a child who never got an antibiotic at all. Therefore, SSLR is an immune response to the infection rather than the antibiotic.
What are the Symptoms of a Serum Sickness-Like Reaction?
Symptoms of SSLR develop seven to 14 days after the start of an infection. Examples are a respiratory infection or strep throat. SSLR may last for several weeks. SSLR typically starts first with itchy rashes that look like hives, either red- or skin-colored welts. They may change into a rash with bruised-looking centers. The rash will go away in five to seven days.
Additional symptoms may develop after the initial rash. This may include swelling of the face, hands and/or feet. Fever, joint stiffness and pain, and/or vomiting may happen as well. Knee or ankle pain may cause infants to refuse to walk or bear weight. Hives or welts may come and go for one to 12 weeks after all other symptoms get better.
Patients and families may be seen by a healthcare provider many days in a row because new symptoms appear. Symptoms of SSLR get worse several days after rash development. SSLR is not life-threatening. It will go away.
How is a Serum Sickness-Like Reaction Treated?
Treatment for serum sickness-like reactions may include a variety of medications prescribed by your doctor. Treat the medications your child is taking as allergies until allergy testing can be done at a later date.
Increased skin sensitivity is common.
- Keep the skin cool and dry. Heat and moisture can make the hives and itching continue or come back.
- Take oatmeal baths one to two times a day to help relieve itching, inflammation and to help soothe the skin. With the water running, sprinkle 1 cup of oatmeal into lukewarm water. Soak for 10-15 minutes and then gently pat the skin dry.
- Keep fingernails filed and trimmed short to prevent any scarring or opening of any raised areas if itching occurs.
- Try not to use any new medications, vaccines and other potential triggers while the SSLR resolves, if possible.
Future Testing
Future testing to find any potential triggers is recommended. Patients and families may feel nervous about giving their child the same antibiotics the child was taking while experiencing an SSLR. But most reactions will not happen again from the same medication.
Testing involves taking the same medication by mouth, done three to six months after the initial SSLR. This depends on the patient’s comfort level and the risks associated with ongoing avoidance.
When to Call the Doctor
If you think your child may have SSLR, or is experiencing any allergic symptoms, call PATS (Penicillin Allergy Testing Service) at 513-517-7287 to set up a same-day telehealth appointment with an allergy provider.
