Inpatient and emergent screening for COVID -19 is evolving and includes rapid antigen and PCR testing. However concerns that cross-reactivity of the COVID antigen test with other innate proteins raises doubt over the utility and reliability of this screening test. 

We present a 52 year old male with a background of rheumatoid arthritis, seizure disorder, chronic nicotine dependence and peptic ulcer disease who was transferred with septic shock for ICU admission. He describes a two day history of pain in both upper limbs starting on the left and then moving to his right arm. He denied any trauma, any sick contacts, any infective symptoms barring a one day history of nasal congestion. He had not been vaccinated for the COVID-19 virus. He lives alone, is an active smoker who admits to occasional use of marijuana. 

On examination he had prominent pain over the left elbow with swelling seen over both wrist joints as well as bilateral plantar wounds. He had overlapping toes with bilateral lung infiltrates and multiple arthritic changes seen on plain radiograph. His chest CT also suggested subpleural emphysema which could be related to underlying arthritis. On admission he had two positive antigen tests but was RNA PCR negative. Subsequently an isothermal PCR which was also negative. He received two days of systemic steroid and tocilizumab for COVID. He was found to have septic arthritis of multiple joints and was taken for drainage of these joints along with debridement of the foot. Multiple sites grew Streptococcus C with MRSA detected in the foot wound. He continues with antibiotic therapy but has had no respiratory compromise. 

Those who suffer with autoimmune disorders exhibit increased frequency of false positive COVID-19 antigen testing. Careful screening of this patient populations should be encouraged.