Outbreaks Shared Between US and Mexico Require Collaboration For Disease Management

An outbreak of dengue in Sonora, Mexico that resulted in 93 travel-associated cases in Arizona between September and December 2014 shows the need for collaboration between public health services in Mexico and the United States in sharing surveillance data to control and treat mosquito borne diseases, according to a study published recently in the US Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report.

Between 2007-2013, there were only 3-10 travel-associated cases of dengue annually in Arizona. Of the 93 identified dengue cases in 2014, a nine-fold increase, 75% were located in Yuma County, which shares a border with San Luis Río Colorado in Sonora. The Aedes aegypti mosquito is endemic in Yuma County and with this surge in travel-associated dengue, local transmission could result, the researchers said.

Jefferson M Jones, MD, of the Arizona Department of Health Services and the Epidemic Intelligence Service at the Division of Scientific Education and Professional Development at the CDC and colleagues conducted passive surveillance to examine the temporal relationship of dengue outbreaks between Yuma County and San Luis Río Colorado. Researchers compared patient characteristics and signs and symptoms of the virus in addition to conducting household-based cluster investigations near reported cases to calculate local transmission risk and find unreported cases.

“Among 194 persons in Yuma County surveyed, 152 (78%) reported travelling to Mexico ≥1 time/month, and elevated Breteau, household and container Aedes mosquito density indices were consistent with an increased risk for dengue transmission, demonstrating that Yuma County is at risk for local DENV transmission,” Dr Jefferson and colleagues reported.

The researchers noted that infection rates may differ between Arizona and Sonora due to environmental and behavioral factors, such as air conditioning, that would make Arizona have a lower rate of local transmission. They also concluded that while rates of dengue were higher in Sonora, the rate of hospitalization was higher in Yuma county – 53% of cases there has hospitalization, while only 21% were hospitalized in San Luis Río Colorado. “This might be because clinicians in Yuma County had a lower threshold for admitting dengue patients to the hospital. In a survey of 197 health care providers in Arizona, lack of confidence to treat mild dengue and severe dengue was reported by 58% and 73% of respondents, respectively,” researchers said.

Three limitations were identified in the study. First, that different surveillance protocols in the 2 areas prevent direct comparison. Second, that because not every household was examined, locally transmitted cases may have been missed. Finally, the investigation was performed during colder months when mosquitos are not as active.

Dr Jones and colleagues said sharing of surveillance data would assist in timely detection of outbreaks that cross the border, and enable public health officials to prompt residents to use better mosquito control through the removal of standing water, the use of insecticides, the use of mosquito repellent, the installation and maintenance of window screens, the use of air conditioning, and the wearing of long sleeves and pants to prevent mosquito bites. In addition, surveillance would set a lower threshold for physicians to conduct dengue testing in patients, resulting in more detectable cases.

“Because Aedes mosquitoes also transmit chikungunya and Zika viruses, there is risk for local transmission of these pathogens and a need for vector control and mosquito bite prevention strategies in the border region,” researchers concluded.

Reference

1. Jones JM, Lopez B, Adams L et al. Binational dengue outbreak along the United States–Mexico border — Yuma County, Arizona, and Sonora, Mexico, 2014. MMWR. 2016; 65(19):495–499.