Clinical malaria along the China-Myanmar border, Yunnan Province, China, January 2011-August 2012.

Passive surveillance for malaria cases was conducted in Yunnan Province, China, along the China-Myanmar border. Infection with Plasmodium vivax and P. falciparum protozoa accounted for 69% and 28% of the cases, respectively. Most patients were adult men. Cross-border travel into Myanmar was a key risk factor for P. falciparum malaria in China.

Increased global efforts to control and eliminate malaria are leading to substantial declines in malaria-related illness and death (). Plasmodium vivax is the predominant malaria-causing species in China, followed by P. falciparum. Cross-border migration from Myanmar is suspected to be the major source for the introduction of P. falciparum malaria in southwestern China. During the past decade, the incidence of malaria in China has declined tremendously; the reduction in Myanmar has been less dramatic (–). To identify risk factors for clinical malaria and, in turn, to inform the ongoing malaria elimination programs in China, we conducted passive surveillance for malaria at health facilities along the China–Myanmar border in Yunnan Province, China, during January 2011–August 2012.

The Study

The Southeast Asia Malaria Research Center (www.niaid.nih.gov/LabsAndResources/resources/icemr/centers/Pages/southeastasia.aspx), an International Center of Excellence for Malaria Research, in collaboration with the Chinese Center for Disease Control and Prevention, conducted passive malaria case detection along the China–Myanmar border. Surveillance was conducted at 60 hospitals and health care centers in Tengchong, Yingjiang, Longchuan, and Ruili Counties in Yunnan Province, China. According to the Sixth National Population Census of the People's Republic of China conducted in 2010 (http://chinadatacenter.org/Announcement/AnnouncementContent.aspx?id=470), the population of the 4 counties totaled ≈1.5 million. During 2010, Ruili and Yingjiang Counties reported the highest incidence of malaria in China ().

Persons who sought care for febrile illnesses at 1 of the 60 surveillance site hospitals or health care centers were screened for clinical signs and symptoms of malaria. Case report forms were used to collect the following information from patients: demographic characteristics, occupation, education level, clinical symptoms, history of malaria in the preceding 12 months, history of travel within the 2 weeks preceding the clinic visit, history of fever, and use of measures to prevent malaria. For each suspected case-patient, thick and thin blood smears were prepared and examined by 3 experienced microscopists to provide a final diagnosis and parasite densities. Patients were considered to have clinical malaria if they had signs and symptoms consistent with malaria and a plasmodium-positive blood smear; severe malaria was defined according to World Health Organization criteria ().

During January 2011–August 2012, a total of 8,296 Chinese and Myanmarese persons sought care for fever at the surveillance sites; 656 (7.9%) of the patients had other signs and symptoms consistent with malaria. Blood smear examination by microscope confirmed malaria infection in 303 (46.1%) of the 656 patients (Table 1). Protozoa of all 4 Plasmodium spp. that cause malaria in humans were detected; however, P. vivax and P. falciparum accounted for 69.0% and 27.7%, respectively, of the cases. Transmission peaked during April–July; cases of P. falciparum infection were detected primarily during the peak season (Figure). Asexual parasite densities were 1,285 and 2,515 parasites/μL, for P. vivax and P. falciparum, respectively. Chinese patients had fever for a median of 3.0 days, and Myanmarese patients (>90% of whom lived in China) had fever for a median of 2.5 days (range 1–10 days; p>0.05) before seeking care at a surveillance site. A total of 4 (1.9%) patients with P. vivax malaria and 13 (15.5%) patients with P. falciparum malaria had severe symptoms at the first clinical visit and were treated as inpatients.

Table 1

Demographic characteristics for participants in a study of clinical malaria along the China–Myanmar border, Yunnan Province, China, January 2011–August 2012*

Characteristic	No. (%) febrile case-patients, n = 8,296	No. (%) suspected cases, n = 656	No. (%) confirmed cases, n = 303	Odds ratio (95% CI)
Nationality
Chinese	6,002 (83)	586 (89)	257 (85)	1
Myanmarese	1,232 (17)	70 (11)	46 (15)	2.5 (1.5–4.1)†
Sex
F	3,648 (44)	88 (13)	27 (9)	1
M	4,629 (56)	568 (87)	276 (91)	2.1 (1.3–3.5)‡
Age, y
<18	1,864 (23)	66 (10)	16 (5)	1
>18	6,359 (77)	590 (90)	287 (95)	3.0 (1.6–5.3)†
Occupation
Indoor worker§	NC	64 (10)	10 (3)	1
Farmer	NC	433 (66)	203 (67)	4.8 (2.4–9.6)†
Business person	NC	78 (12)	41 (14)	6.0 (2.7–13.4)†
Mobile worker¶	NC	78 (12)	49 (16)	9.1 (4.0–20.6)†
Use of preventive measures#
No	NC	257 (39)	209 (69)	1
Yes	NC	399 (61)	94 (31)	0.07 (0.05–0.10)†

*For some case reports, information was missing for nationality, sex, age, or occupation. NC, not calculated because information was missing for a considerable number of febrile cases.
†p

Figure

Number of confirmed malaria cases caused by various Plasmodium spp. protozoa in 4 counties of Yunnan Province, China, along the China–Myanmar border, January 2011–August 2012. Mixed, P. vivax/P. falciparum infection.

*For some case reports, information was missing for nationality, sex, age, or occupation. NC, not calculated because information was missing for a considerable number of febrile cases.
†p