[Epidemiological characteristics of imported malaria cases in Shanghai Municipality from 2020 to 2024]

To investigate the epidemiological characteristics of imported malaria cases in Shanghai Municipality from 2020 to 2024, so as to provide insights into dynamic adjustment of imported malaria control strategies.

All data pertaining to malaria cases reported in Shanghai Municipality from 2020 to 2024 were collected from Infectious Diseases Reporting Information Management System and Parasitic Diseases Prevention and Control Information Management System of Chinese Center for Disease Control and Prevention, and epidemiological investigation reports of malaria cases. The type of malaria cases, source of acquiring infections, temporal, spatial and population distributions of malaria cases, type of initial diagnosis institutions, accuracy of initial diagnosis, time interval from disease onset to initial diagnosis, and the time interval from initial diagnosis to diagnosis were statistically analyzed. The monthly distribution of malaria cases was analyzed using a circular distribution method.

A total of 124 malaria cases were reported in Shanghai Municipality from 2020 to 2024, with 14, 52, 22, 8 and 28 cases annually, respectively, and all cases were overseas imported cases. Plasmodium falciparum malaria was the predominant type, accounting for 82.26% (102/124) of all malaria cases, while P. ovale, P. vivax and P. malariae malaria accounted for 8.06% (10/124), 7.26% (9/124) and 2.42% (3/124) of reported cases, respectively. Malaria cases acquired infections from 28 countries in 4 continents, with African countries as a major source of acquiring infections (96.77%, 120/124). Malaria cases were reported across all 16 districts in Shanghai Municipality. There were peaks in numbers of reported malaria cases in May 2021 (9 cases) and November 2021 (9 cases); however, there was no concentration trend in the reporting time of malaria cases from 2020 to 2024 (Z = 2.45, P > 0.05). The reported malaria cases included 116 males and 8 females, with a male-to-female ratio of 14.5∶1.0, and had a median age of 39 (17) years. Worker was the primary occupation of reported malaria cases, accounting for 48.39% (60/124) of all reported cases. City-level medical institutions were the predominant initial diagnosis institutions (75.81%, 94/124). The overall accuracy of initial diagnosis was 74.19% (92/124), and the median time interval from disease onset to initial diagnosis was 0 (2) day (healthcare seeking on the day of disease onset), with 72.58% (90/124) of malaria cases seeking healthcare services within one day. The median time interval from initial diagnosis to diagnosis was 2 (3) days, with 41.94% (52/124) of malaria cases that were definitively diagnosed within one day following initial diagnosis. There were significant differences in the accuracy of initial malaria diagnosis (χ² = 15.01, P < 0.05), the time interval from disease onset to initial diagnosis (H = 29.30, P < 0.001), and the time interval from initial diagnosis to diagnosis (H = 22.92, P < 0.001) among years from 2020 to 2024, and the time interval from disease onset to initial diagnosis (Z = -5.09, P < 0.001) and the time interval from initial diagnosis to diagnosis (Z = -4.14, P < 0.001) were both shorter during the period from 2020 to 2022 than those recorded from 2023 to 2024. In addition, a total of 2 malaria deaths were reported in Shanghai Municipality during the period from 2020 to 2024, both caused by P. falciparum malaria.

The numbers of malaria cases fluctuated continuously in Shanghai Municipality from 2020 to 2024. It is recommended to continuously strengthen surveillance and response measures, improve malaria diagnosis and treatment capabilities, and conduct targeted health education activities among high-risk populations, such as labors going to overseas malaria hyper-endemic areas, so as to prevent re-establishment of imported malaria.