An epidemiological analysis of imported malaria in Shanghai during a COVID-19 outbreak.

Background: The goal of this study was to understand the epidemiological characteristics of imported malaria in Shanghai specifically during the epidemic period of novel corona-virus pneumonia (COVID-19), to provide a reference for preventing the transmission of imported malaria after this disease had been previously eliminated.

Methods: The data of malaria cases reported in Shanghai from 2020 to 2021 were obtained from the China Information System for Disease Control and Prevention (CISDCP) and the Information System for Parasitic Disease Control and Prevention (ISPDCP). The characteristics of demographic and epidemiological distribution, travel-related information, diagnosis information, regions of infection acquisition and disposal information of epidemic situation were analysed with descriptive statistics.

Results: A total of 112 cases of malaria were reported in Shanghai from January 2020 to December 2021. There were 18 cases and 94 cases in 2020 and 2021, respectively, reaching the lowest and highest levels in the past 10 years. The incidence of malaria associated with seasons had an increasing trend (χ = 81.143, P < 0.05). These cases included Plasmodium falciparum (97, 86.61%), Plasmodium vivax (4, 3.57%), Plasmodium ovale (8, 7.14%) and Plasmodium malariae (3, 2.68%). The median age of patients with malaria was 38.0 years, the majority of these individuals were males (109, 97.32%), and most of them were labour personnel (93, 83.04%). Of the reported cases, 8 of these individuals (7.14%) reported experiencing malaria symptoms before their arrival in China after their stay overseas; 97 of these individuals (86.61%) reported experiencing symptoms within 14 days after their initial arrival from overseas; 15 of these individuals (13.39%) were diagnosed with 'severe malaria'; and 4 of these individuals (3.57%) were also diagnosed with COVID-19. All cases were imported from Africa, and there were no indigenous cases and deaths.

Conclusion: Due to the impact of COVID-19, the number of imported malaria cases in Shanghai had greatly increased; however, prevention and control measures for imported malaria could be implemented to prevent re-transmission of this condition. Considering that the number of individuals returning from overseas labour is likely to increase in the next few years, it is necessary to strengthen the surveillance of imported malaria and to review the protocol for potential epidemic situations. Together, these measures could support the maintation of free-malaria status in Shanghai.