Bulletin of the World Health Organization

Estimated global incidence of Japanese encephalitis: a systematic review

Grant L Campbell, Susan L Hills, Marc Fischer, Julie A Jacobson, Charles H Hoke, Joachim M Hombach, Anthony A Marfin, Tom Solomon, Theodore F Tsai, Vivien D Tsu & Amy S Ginsburg

Volume 89, Number 10, October 2011, 766-774E

Table 2. Summary of the 12 primary references used to estimate the incidence of Japanese encephalitis (JE) in Asia, by incidence group

IG Country Reference Study type Laboratory-confirmed
Study period Study area Study age group Estimated study population Estimated annual incidencea Relative quality of study data
No. %
A Japan Arai et al. (2008)23 Routine (passive) national surveillance 53 100 1992–2004 (13 years) Entire country All 126.4 million (approx. mid-interval population) 0.003 Medium-quality data from national surveillance system based on physician reports of laboratory-confirmed cases; caveats include that laboratory methods used have evolved over time.
Hashimoto et al. (2007)24 Routine (passive) national surveillance 33 100 2000–2005 (6 years) Entire country All 126.55 million 0.004 Medium-quality data from national surveillance, based on laboratory confirmation of physician-reported, clinically suspected cases.
C1 China Yin et al. (2010)20 Multiple hospital-based surveillance 121 100 Apr. 2007 to Sept. 2008 (17 months) or Sept. 2006 to Sept. 2008 (25 months), depending on prefecture Guigang prefecture, Guangxi province; Yichang prefecture, Hubei province; Jinan prefecture, Shandong province All 14.13 million 0.6b Medium-quality data from 6 carefully selected sentinel hospitals in each prefecture; caveats include that not all hospitals in each prefecture were included.
Xufang et al. (2010)13 Multiple hospital-based surveillance 1609 75 2006 (1 year)c Guizhou province All 37.6 million 4.3 Medium-quality data; all hospitals in the province were included in surveillance, but samples were unavailable for testing in 25% (455/1837) of clinically suspected cases, so incidence estimate was adjusted upward, based on seropositivity rate among those tested.
C2 China Yin et al. (2010)20 Multiple hospital-based surveillance 18 100 Apr. 2007 to Sept. 2008 (17 months) Shijiazhuang prefecture, Hebei province All 5.06 million 0.01d See above.
D Cambodia Touch et al. (2009)25 Multiple hospital-based surveillance 583e 19 2007 (1 year) Entire country 0–14 years 5.25 million 11.1 Medium-quality data from 6 carefully selected sentinel hospitals distributed throughout the country.
Indonesia Kari et al. (2006)26 Multiple hospital- and clinic-based enhanced (active) surveillance 90 100 July 2001 to Dec. 2003 (2.5 years) Bali province 0–11 years 599 120 6.0 High-quality data; all health care facilities in the province providing care for the study population were included in active surveillance system.
Thailand Hoke et al. (1988)27,f Vaccine trial; enhanced (active) local public health surveillance 11 100 1985–1986 (2 years) Kampangphet province 1–14 years 21 516 25.6 High-quality data; all health care facilities in the province providing care for the study population were included in active surveillance system.
F Nepal Partridge et al. (2007)28 Multiple hospital-based surveillance 225 (100) 2006 (1 year) Terai & Inner Terai districts (n = 24) All 12.46 milliong 1.8 Medium-quality data from national surveillance system, based on laboratory confirmation of clinically suspected cases using an incomplete network of 93 hospitals and clinics; caveats include that specimens for laboratory testing were unavailable in 16% of clinically suspected cases, with no adjustment for this potential source of underdiagnosis.
Wierzba et al. (2008)29 Multiple hospital-based surveillance 951 100 May 2004 to Apr. 2006 (2 years) Terai & Inner Terai districts (n = 24) All 12.46 milliong 3.8 Medium-quality data from national surveillance system, based on laboratory confirmation of clinically suspected cases using an incomplete network of 64 hospitals; caveats include that specimens for laboratory testing were unavailable in 31% of clinically suspected cases, with no adjustment for this potential source of underdiagnosis.
G Bangladesh Paul et al. (in press)30 Multiple hospital-based surveillance 472d 8 Oct. 2007 to Dec. 2008 (15 months) Bagerhat, Chittagong, Cox's Bazar, Jessore, Jhenaidah, Khulna, Naogaon, Narail, Nawabganj, Rajshahi, & Satkhira districts All 27.5 million 1.4d Relatively lower quality data because incidence was not directly measured, but rather extrapolated retrospectively from hospitalized, laboratory-confirmed cases to non-hospitalized, clinically suspected but laboratory-untested patients.
Nepal Partridge et al. (2007)28 Multiple hospital-based surveillance 67 100 2006 (1 year) Mountain and hill (non-Terai) districts (n = 51) All 10.69 milliong 0.6 See above.
Wierzba et al. (2008)29 Multiple hospital-based surveillance 84 100 May 2004 to Apr. 2006 (2 years) Mountain and hill (non-Terai) districts (n = 51) All 10.69 milliong 0.4 See above.
Bhattachan et al. (2009)31 Multiple hospital-based surveillance 90 100 2007 (1 year) Mountain and hill (non-Terai) districts (n = 51) All 10.69 milliong 0.8 Medium-quality data from national surveillance system, based on laboratory confirmation of clinically suspected cases using an incomplete network of hospitals; specimens for laboratory testing were available in 96% of clinically suspected cases.
H Malaysia Wong et al. (2008)32 Single hospital-based surveillance 49 100 July 2001–2006 (post-vaccine programme) (5.5 years) Sibu Hospital, Sarawak state All 600 000 (in catchment area) 1.5 Medium-quality data from a single, central, large, sentinel hospital; caveats include that incidence estimates were apparently based on the assumption that 100% of JE cases in this hospital’s catchment area would present to this hospital, and that none from outside the catchment area would do so.

IG. incidence group.

a Per 100 000.

b Weighted average of results from all three prefectures (using raw incidence data, as data used in their adjustment of incidence rates were not provided).

c April to November, but because this timeframe brackets the JE transmission season in the region, 1 year was used.

d Using raw incidence data, as data used in their adjustment of incidence rates were not provided.

e 100% of study cases were laboratory-confirmed; the study's authors then extrapolated their results to a larger geographic area, proportionate to the total number of acute encephalitis syndrome cases reported.

f These historical, pre-vaccination-era data from Thailand were used, in part, to estimate incidence in Incidence Group D, but present-day Thailand was included in Incidence Group H.

g 2001 census data.