RESUMEN
Background: COVID-19 has had a significant public health impact on both the United States and Mexico. Cross-border mobility between southern California and Mexico raises questions of transmission trends between these jurisdictions. The objective of this project was to describe binational cases amongst California US-Mexico border county COVID-19 cases and compare incidence trends to cross-border Mexico jurisdictions. Methods: Interview data from persons with confirmed SARS-CoV-2 infections in San Diego County, CA and Imperial County, CA from February to June 2020 were reviewed for binational cases; demographics and connection to COVID-19 outbreaks were assessed. Graphs of COVID-19 incidence in San Diego County and Imperial County were compared to incidence graphs in cross-border Mexico jurisdictions of Tijuana and Mexicali. Results: Persons with COVID-19 and a binational case were older, more likely to be Hispanic, and reside in a border ZIP code than those without. Binational cases were a small proportion and tracked with overall cases during the study period. Conclusions: Binational cases had different trends than non-binational cases of SARS-CoV-2 in San Diego and Imperial counties from February to June 2020. Findings could inform SARS-CoV-2 mitigation strategies specific to the US-Mexico land border, particularly recommendations regarding cross-border land travel.
RESUMEN
BACKGROUND: Dogs are vulnerable to pathogens transmitted by brown dog ticks. An epidemic of Rocky Mountain spotted fever (RMSF) is underway in Mexicali, a Mexican city bordering California affecting people and dogs; several human cases have been reported in California residents who travelled to Mexico. To evaluate risks of RMSF, we conducted seroprevalence surveys in Imperial County in 2016 and 2017 using dogs as sentinels. METHODS: Blood was collected from 752 dogs and was tested for antibodies against R. rickettsii, E. canis and A. phagocytophilum (as a proxy for A. platys). Samples were considered seropositive to spotted fever group rickettsia (SFGR) if the R. rickettsia titre was ≥1:64 and seropositive to E. canis and A. phagocytophilum if the titre was ≥1:32. Owners provided information on dog age, exposure risks, health status and tick prevention. We assessed associations between SFGR seropositivity and driving distance to the nearest US-Mexico border crossing station, whether proximity to a border crossing increased likelihood of taking dogs across the border, and whether distance to the border was associated with seropositivity. Logistic regression was performed to assess relationships between the titre classes and other predictor variables. RESULTS: 12.2% of dogs were seropositive against SFGR. Dogs close to the border were significantly more likely to be taken across the border and to be seropositive. Risk factors that increased seropositivity included owners seeing ticks on the dog (OR = 1.9), being an adult dog, travel to Mexico (OR = 3.0) and living in a rural area (OR = 4.0). There was statistically significant co-exposure to SFGR and Anaplasma spp. CONCLUSION: Surveillance for brown dog tick-vectored pathogens can help identify dogs and people at risk for RMSF. Tick prevention, particularly in dogs, and surveillance of tick-borne pathogens can help prevent the spread of rickettsioses and other diseases in this dynamic border region.