Hot spot detection and spatio-temporal dispersion of dengue fever in Hanoi, Vietnam

Figures & data

Fig. 1.  Location of the study area – Hanoi, Vietnam.

Table 1. Descriptive statistics of monthly numbers of postcode areas with notified dengue cases

Period	Mean	SD	Minimum	Q1^a	Median	Q3^b	Maximum
2004–2005	41.00	32.36	5	15.75	36	59	95
2006–2007	49.33	32.47	8	24.25	47	72.25	104
2008–2009	79.33	45.53	17	36.75	74	122.5	146

^aQ1, first quartile value.

^bQ3, third quartile value.

Fig. 2.  Numbers of dengue cases (^____) and postcode areas with dengue notifications (-----) between January 2004 and December 2009 in Hanoi.

Fig. 3.  Boxplots of the seasonal distribution of numbers of postcode areas with dengue infection in three periods in Hanoi. The boxplots display the values of the 25th, 50th, and 75th percentiles.

Fig. 4.  Map showing raw dengue incidence rates in three periods.

Table 2. Spatial autocorrelation analysis for dengue in Hanoi, 2004–2009

Period	Annual incidence	Moran's I	E(I)	p
2004–2005	226.32	0.19	−0.011	0.001
2006–2007	1049.78	0.32	−0.007	0.001
2008–2009	3774.49	0.22	−0.006	0.001

Table 3. The clusters of dengue cases detected using the purely temporal analysis

Year	Cluster time frame	Total days of cluster	Obs^a	Exp^b	Relative risk	LLR^c	p
2004	4/8–1/12	118	216	160.30	1.90	17.68	0.001
2005	5/6–1/12	177	246	167.56	14.26	74.0	0.001
2006	5/6–1/12	177	1,679	1,556.38	2.30	45.39	0.001
2007	5/7–31/12	177	1,051	937.56	1.88	33.36	0.001
2008	4/8–16/12	133	992	886.41	1.60	23.84	0.001
2009	20/6–16/12	179	7,725	7,634.84	1.34	12.64	0.001

^aThe number of observed cases in a cluster.

^bThe number of expected cases in a cluster.

^cLog likelihood ratio.

Table 4. The clusters of dengue cases detected using the purely spatial analysis

Year		Location	Obs^a	Exp^b	Relative risk	LLR^c	p
2004	A	Thanh Tri	175	150.08	1.33	3.56	0.932
2005	A	Hai Ba Trung, Hoang Mai	65	37.10	2.01	10.4	0.002
	B	Thanh Xuan, Dong Da	128	96.19	1.66	8.18	0.017
2006	A	Dong Da, Tay Ho, Long Bien	833	806.05	1.06	0.81	1.000
2007	A	Dong Da, Ba Dinh	658	609.28	1.17	3.89	1.000
2008	A	Tu Liem, Cau Giay	238	215.30	1.13	1.41	1.000
2009	A	Hoan Kiem, Hai Ba Trung	2,346	2323.1	1.02	0.16	1.000

^aThe number of observed cases in a cluster.

^bThe number of expected cases in a cluster.

^cLog likelihood ratio.

A: Most likely cluster; B: Secondary cluster.

Table 5. SaTScan statistics for space–time clusters with significantly higher incidence in Hanoi from 2004 to 2009 (most likely cluster)

Location	Radius (km)	Time frame	Relative risk	p
Hoang Mai	2.50	4/8–19/7/2004	2.03	0.001
Thanh Xuan	0.68	17/11–31/12/2005	2.66	0.001
Dong Da	0.64	2–16/11/2006	3.51	0.001
Dong Da	0.99	17/11–16/12/2007	3.38	0.001
Hoang Mai	0.29	19/8–2/10/2008	5.58	0.001
Hoan Kiem, Hai Ba Trung	1.56	2–16/11/2009	6.41	0.001

Fig. 5.  Scatterplot of significant space–time clusters in Hanoi from 2004 to 2009.

Table 6. Changes of dengue fever in latitude and longitude, Hanoi, 2004–2009

	Latitude		Longitude
Change in periods	OR	95% CI	OR	95% CI
Period 3–Period 1	1.17	1.02–1.34	1.06	0.93–1.34
Period 2–Period 1	0.94	0.85–1.03	0.98	0.87–1.11
Period 3–Period 2	1.09	0.99–1.22	0.98	0.89–1.06

Note: Period 1: 2004–2005; Period 2: 2006–2007; Period 3: 2008–2009.