Abstract:

In order to understand the epidemiological characteristics of imported malaria after malaria elimination in Longgang District of Shenzhen City and analyze the effect of epidemic surveillance and response, the surveillance data of malaria in Longgang District from 2018 to 2023 were collected from the National Information System for Infectious Diseases Surveillance， National Information System for Parasitic Diseases Control and Prevention, as well as medical institutions and annual reports. The vehicle monitoring was carried out. Descriptive epidemiological methods were used to analyze the data, such as the number of cases, parasite species, infection sources, clinical symptoms, and surveillance data. The results showed that 173 imported malaria cases were reported in Longgang District from 2018 to 2023, including 144 cases of Plasmodium falciparum infection (83.2%), 13 cases of P. ovale infection(7.5%), 11 cases of P. vivax infection (6.4%), 1 case of P. malariae infection (0.6%), and 4 cases of mixed infection with P. falciparum and P. ovale (2.3%). The main infection sources were Africa (169 cases, 97.7%) and Southeast Asia (4 cases, 2.3%). There were 7 outpatients (4.0%) and 166 inpatients (96.0%), including 1 severe case (0.6%). The number of imported cases peaked in July, August and October (21, 51 and 20 cases), and February saw the fewest cases (2 cases). Most of the reported cases were young and middle-aged males, with a male-to-female ratio of 13.4 ∶ 1. From 2018 to 2023, the positive rate of Plasmodium blood smears in Longgang District was 6.0‰ (173/29 025), and the average time from initial diagnosis to definitive diagnosis decreased from 2.32 d during 2018-2020 to 0.58 d during 2021-2023 (t = 2.102, P < 0.05). The correct rate of initial diagnosis was 96.4% (135/140) at the city level, 69.0% (20/29) at the county level, and 0/4 at community health service centres and other medical institutions (Fisher’s exact test, P < 0.01). The correct rates of microscopic examinations for P. falciparum, P. malariae, P. vivax, P. ovale and mixed infections were 88.9% (128/144), 1/1, 11/11, 8/13 and 2/4, the difference was statistically significant (Fisher’s exact test, P < 0.01). All the cases were reported within 1 day, and after finishing laboratory review, epidemiological investigation and case report within 3 days, all the epidemic spots were disposed of within 7 days. None of the cases gave rise to secondary cases. Anopheles mosquitoes were not found in Longgang from 2018 to 2023. Longgang District is under great pressure for the prevention and control of imported malaria after malaria elimination. The malaria surveillance and response system in medical and disease control institutions operates well. However, the capacity for malaria diagnosis, treatment, and laboratory testing among the medical staff and institutions should be further improved.

Key words: Imported malaria, Post-elimination, Surveillance and response, Epidemiological characteristics