Notes from the Field: Increase in Reports of Strongyloides Infection — Los Angeles County, 2013–2014

Curtis Croker, MPH1; Rosemary She, MD2

During the 1990s, reports of infection with the nematode (roundworm) Strongyloides stercoralis submitted to the Los Angeles County Department of Public Health (LACDPH) ranged from 40 to 50 per year, but by 2000, reports had decreased to five per year; in 2006, Strongyloides infection was removed from the LACDPH reportable disease list. Currently, it is only reported at the discretion of Los Angeles County clinicians and laboratories as an unusual disease occurrence. LACDPH currently only monitors case counts and does not investigate reported Strongyloides cases. During 2013–2014, an increase in Strongyloides cases occurred, with 43 cases reported.

Although Strongyloides infects humans worldwide, typically through skin contact with contaminated soil (1), infection is rare in the United States. Persons at risk for infection include immigrants, refugees, military veterans who have lived in areas where Strongyloides is endemic, (1) and persons who have lived in rural areas of the southeastern United States (2). Most infections are asymptomatic and might remain latent for decades. Persons with latent infection who receive immunosuppressive treatments or are otherwise immunosuppressed are at risk for a severe hyperinfection syndrome and disseminated disease, which is associated with a high mortality rate (3). During 1991–2006, the number of Strongyloides-associated deaths in the United States listed on death certificates ranged from 14 to 29 annually (4). Eosinophilia is the most common indicator of infection, but it is not specific to this disease and is not always present (5).

Beginning in 2013, Strongyloides case reports in Los Angeles County increased; no cases were reported in 2012, but 14 were reported in 2013 and 29 in 2014. Twenty-five (58%) of these reports were submitted by CDC's parasitic serology reference laboratory, for patients examined at Los Angeles County–University of Southern California Medical Center (LAC-USC). Sixteen reports were submitted by refugee health clinics, and two by other health care providers. The increase in case reports prompted a review of the 25 patients with Strongyloides examined at LAC-USC, a facility that accounts for 3% of all hospitalizations in a county of nearly 10 million residents.

The patients with Strongyloides examined at LAC-USC were mostly male (76%), Hispanic (80%), or Asian (16%). Most were foreign born (75%), primarily from a Latin American country (60%). The average patient age was 50 years (median = 55 years; range = 25–73 years). All patients tested positive for Strongyloides-specific antibody by enzyme immunoassay (EIA) testing performed by the CDC reference laboratory, indicating current or recent infection (6). The average test reaction value was 25.76 units/µl (range = 2.37–75.58 units/µl; reference 1.7 units/µl). Four were immunocompromised. Three patients were hospitalized at the time of testing; no patient had a diagnosis of disseminated disease or hyperinfection.

Of the 25 patients, 21 (88%) had peripheral eosinophilia (>450 eosinophils/µl) at the time of Strongyloides testing; the average eosinophil count was 1,297/µl (range = 201–3,472/µl). Nearly all patients (96%) had documentation of eosinophilia at some point during the 6 months preceding Strongyloides testing. Most were tested in an outpatient facility (88%), and many were being followed for other chronic health conditions such as hypertension (52%) or diabetes (48%), where eosinophilia appeared to be an incidental finding. Treatment was documented for 17 patients (68%), consisting of ivermectin alone for 15 patients, albendazole alone for one patient, and both drugs for one patient.

The recent increase in reports of Strongyloides in Los Angeles County is likely the result of screening guidelines published in 2012, which recommend screening all persons with a potential Strongyloides exposure history who are at risk for disseminated disease, including persons requiring immunosuppressive therapy (7), and changes in existing screening protocols, rather than an actual increase in disease prevalence. The high prevalence of eosinophilia among persons with latent Strongyloides infection in Los Angeles County highlights the importance of screening persons with eosinophilia for whom more common causes have been ruled out. Diagnosis of latent infection is important so that treatment can be initiated and the risk for more severe disease eliminated, and is crucial for persons with unexplained eosinophilia who will be placed on immunosuppressive drug regimens (7).

The burden of disseminated disease and hyperinfection in Los Angeles County remains unknown. Further research is needed to better characterize the at-risk group in Los Angeles County and enhance screening policies.

1Acute Communicable Disease Control Program, Los Angeles County Department of Public Health, California; 2Keck School of Medicine of the University of Southern California, Los Angeles, California.

Corresponding author: Curtis Croker, ccroker@ph.lacounty.gov, 213-240-7941.

References

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