A description of the first known case of Zika virus in a U.S. resident returning from Costa Rica has been released in the Annals of Internal Medicine. The individual was a previously healthy 55 year-old male, who presented at Mount Auburn Hospital in Cambridge, MA, on January 2. He informed clinicians how he began feeling mild myalgia and fever starting on December 30, and that he had spent the December 19–26 in Costa Rica with 2 family members. He reported having many mosquito bites. 

The patient had a maculopapular rash involving the face, trunk, and arms as well as headache and arthralgia. Lab tests showed leukopenia, lymphopenia, and bandemia. Tests showed he was negative for streptococcal and malaria. Serologic testing for antibodies for dengue and chikungunya viruses were sent, and negative results were reported 2 weeks later.

On January 7 — Day 9 of his illness — the patient was evaluated at the Mount Auburn Hospital Travel Medicine Center. He had no fever but was experiencing backache, nonpurulent conjunctivitis, and a faint residual erythematous maculopapular rash on the face and trunk. His leukopenia, lymphopenia, and bandemia had resolved. 

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Enzyme-linked immunosorbent assay for IgM antibodies and plaque reduction neutralization antibody tests for Zika and dengue viruses were done at the Centers for Disease Control and Prevention (CDC). On January 26, IgM antibodies to Zika and dengue viruses were reported positive. Plaque reduction neutralization antibody test titers were >5120 for Zika virus and <10 for dengue virus.

On January 25 — Day 27 of his illness —the patient recovered completely. As of February 8, the 2 people who had traveled to Costa Rica with him in December were healthy. Zika virus infection had not been documented in Costa Rica as of January 26, when infection in this patient was confirmed.

According to the Annals, the consequences of this patient’s case suggest that Zika virus is likely circulating more widely than has been officially reported. It also highlights travelers as potential carriers and instigators of spreading pathogens to new geographical areas.

For more information visit annals.org.