The Immigration and Customs Enforcement announced on Friday that more than 5,000 migrants exposed to infectious diseases have been placed in quarantine. The agency said there have been cases of either mumps or chicken pox in 39 different detention centers.

“The preponderance of evidence points to the major influx at our Southwest border being, at minimum, a significant contributing factor of these occurrences,” Nathalie Asher, executive associate director for ICE’s Enforcement and Removal Operations, said in a statement. A total of 5,200 detainees have been quarantined, including 4,200 are for exposure to mumps and 800 who were exposed to chicken pox and 100 have been exposed to both, the agency said.

Last week President Trump announced a deal with Mexico to help curb the number of Central Americans coming through Mexico to request asylum in the U.S. On Friday, the Mexican government released the details of a “side deal” made with Trump that includes some additional measures.

The supplementary agreement signed June 7 between the two countries shows that Mexico will require migrants fleeing their homelands through Mexico to seek asylum there. Mexico agreed to examine domestic laws and regulations to identify necessary changes to implement the side agreement. The provisions included in the side agreement released Friday call for “burden-sharing and the assignment of responsibility for processing refugee claims” from migrants, part of a regional approach to tackling a rise in Central American migration to the U.S.