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Hainan Province is in a tropical area of China and previously experienced serious P. falciparum and P. vivax malaria epidemics. After nearly 70 consecutive years of malaria prevention and control, malaria in Hainan has gradually been eliminated. To achieve the elimination of malaria, Hainan enacted six stages: investigative research and pilot prevention and control, large-scale antimalaria measures, adjustment of strategies for prevention and control, joint prevention and control measures, global funding of routine malaria control, and malaria elimination. Different strategies for malaria control were adopted at different stages. Malaria was most prevalent in the mountainous areas of central and southern Hainan, which contain a high-risk population (the forest goers) and two highly effective malaria vectors (An. dirus and An. minimus). Forest goers have been a high-risk population for malaria in Hainan since their identification in the 1990s. This paper summarizes malaria monitoring in forest goers and the response of forest goers to malaria control and elimination, distilling specific malaria control and elimination measures via case studies in Hainan Province. Two case studies in the malaria control stage demonstrated different measures for outbreaks and sporadic cases in forest goers. In view of the malaria outbreak in Sanya during the elimination stage, three-layered strategies (TLSs) were implemented to control outbreaks and improve control measures. Moreover, this paper also illustrates specific management measures to prevent malaria retransmission from sporadic imported malaria cases during the elimination phase. Hainan finally eliminated malaria in 2020. However, the risk of malaria retransmission is still high due to the prevalence of effective malaria vectors in Hainan, and forest goers are still a high-risk population for malaria retransmission.

BackgroundForest-goers have been the most severely infected by malaria in Hainan since the 1990s. In 2015, there were successively 6 cases of P. malariae infection as an outbreak by forest-goers in Sanya city, Hainan Province. According to the 1-3-7 approach, active case detection(ACD) was performed with guidance from information from Case 1. Cases 2-4 had the same epidemiological history as Case 1 and were similarly confirmed to be infected with P. malariae. However, the clues from Case1 came to an end and it was uncertain whether there were other potential infection sources or whether transmission was established in local villages. MethodsThere was no detailed strategy for the outbreak until 2015, although the 1-3-7 approach was certified to be effective for sporadic case. A retrospective study was conducted on this epidemic of P. malariae transmission among forest-goers in Hainan, 2015. A three-layer strategy (TLS) that integrated malaria joint prevention and control strategies(JPCS) and the 1-3-7 approach was first generated and applied to the disposal of the outbreak in Sanya in 2015, and its was also applied to strengthen epidemic measures to prevent emergence by residual foci from 2016 to 2018. The data were entered by Microsoft Office Excel 2007 for collection and statistic analysis by SPSS.ResultsWith guideline of TLS, three villages in Gaofeng town, Sanya city and Seven villages in Xinzheng Town, Baoting County, were selected as the first layer with design of TLS. In the first layer, 1,823 blood slides and PCR screening from villages in Baoting and Sanya were conducted on all residents by active case detection (ACD) and four cases were identified. In the second layers, passive case detection (PCD) and ACD for forest-goers were conducted and 7,831 blood slides were screened on all forest-goers. In the third layer, PCD was conducted for forest-goers, and 95,350 blood slides were screened on all forest-goers. Meanwhile, vector surveillance and control were also conducted to support foci disposals and to minimize the possibility of transmission. From 2016 to 2018, TLS was also applied to strengthen epidemic measures to prevent emergence by residual foci. In the first layer, chemoprophylaxis and ACD were conducted on residents in the villages of the foci and the surrounding villages, and 89.5% residents accepted chemoprophylaxis. Chemoprophylaxis and ACD were conducted and 79.1% received chemoprophylaxis while seeking forest-goers in the second layer. In the third layer, 89.6% received chemoprophylaxis while seeking forest-goers. ConclusionsThe innovative strategy of TLS not only was successfully applied in an epidemic response strategy in Sanya in 2015 but also was implemented in a strengthened intervention on forest-goers from 2016 to 2018 and finally achieved the goal of eliminating malaria in 2020 as scheduled. TLS is suitable for outbreak by indigenous case of unknown causes or for sporadic cases with defects in epidemic information, while 1-3-7 approach is suitable for sporadic cases which have clearly epidemic clues. Furthermore, TLS could be one of the major achievements after 1-3-7 approach, targeting outbreak in elimination malaria.