Epidemiology of Malaria in Yulin, South China 1999-2016: Imported Malaria Threatens Zero Local Case Status.

OBJECTIVES: This article describes the epidemiology of malaria in Yulin, 1999-2016. We review also malaria control strategy in Yulin in the posteradication phase.

MATERIALS AND METHODS: We examined all malaria case records from Yulin prefecture reported to the Ministry of Health since 1999 and extracted malaria data between 1999 and 2003, the stage of malaria eradication, from the notifiable disease reporting records and case records of Guangxi. Malaria data between 2004 and 2016, the stage of malaria elimination, was obtained from the National Notifiable Disease Reporting System and National Malaria Reporting System. We collected mosquitoes with light traps in the vector-breeding seasons and did the distinguished work with optical microscope.

RESULTS: Malaria average incidence decreased to 0.085/100,000, peaking of 0.263/100,000 in 2006, and no cases in years 2001, 2009, and 2010. Peak seasons are in November and June with proportions of 16.48% and 14.29%, respectively. Pathogenic parasites differed in the two stages; Plasmodium vivax was prevalent between 1999 and 2010, and Plasmodium falciparum between 2011 and 2015. Most malaria cases in the last 18 years occurred in males between 20 and 50 years of age. Of the 91 malaria cases acquired outside Yulin between 1999 and 2016, 31.87% were acquired in other provinces of China, and 68.13% were acquired in foreign countries. Sporozoite-positive vectors were zero between 1999 and 2016.

CONCLUSION: In Yulin, between 1999 and 2016, autochthonous malaria cases decreased to zero. The personal preventative measures of surveillance-treatment-follow-up have been demonstrated to be effective in the Yulin malaria elimination campaign between 1999 and 2016. The major threat of malaria reintroduction to Yulin lies in imported malaria, especially by returning employees working in epidemic areas such as Africa and Southeast Asia. Data concerning employees who have worked abroad should be gathered to enable the construction of a mathematic model to forecast future trends of malaria in Yulin. The antimalaria campaign has to work closely with local authorities.