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Dengue dynamics in Binh Thuan province, southern Vietnam: periodicity, synchronicity and climate variability.

Thai KT, Cazelles B, Nguyen NV, Vo LT, Boni MF, Farrar J, Simmons CP, van Doorn HR, de Vries PJ - PLoS Negl Trop Dis (2010)

Bottom Line: The 2-3-year periodic wave was moving towards, rather than away from Phan Thiet district.A multi-annual mode of oscillation was observed and these 2-3-year waves of infection probably started outside Binh Thuan province.Further studies on an extensive time series dataset are needed to test the hypothesis that epidemics emanate from larger cities in southern Vietnam.

View Article: PubMed Central - PubMed

Affiliation: Division of Infectious Diseases, Tropical Medicine and AIDS, Academic Medical Center, Amsterdam, The Netherlands. khoat@oucru.org

ABSTRACT

Background: Dengue is a major global public health problem with increasing incidence and geographic spread. The epidemiology is complex with long inter-epidemic intervals and endemic with seasonal fluctuations. This study was initiated to investigate dengue transmission dynamics in Binh Thuan province, southern Vietnam.

Methodology: Wavelet analyses were performed on time series of monthly notified dengue cases from January 1994 to June 2009 (i) to detect and quantify dengue periodicity, (ii) to describe synchrony patterns in both time and space, (iii) to investigate the spatio-temporal waves and (iv) to associate the relationship between dengue incidence and El Niño-Southern Oscillation (ENSO) indices in Binh Thuan province, southern Vietnam.

Principal findings: We demonstrate a continuous annual mode of oscillation and a multi-annual cycle of around 2-3-years was solely observed from 1996-2001. Synchrony in time and between districts was detected for both the annual and 2-3-year cycle. Phase differences used to describe the spatio-temporal patterns suggested that the seasonal wave of infection was either synchronous among all districts or moving away from Phan Thiet district. The 2-3-year periodic wave was moving towards, rather than away from Phan Thiet district. A strong non-stationary association between ENSO indices and climate variables with dengue incidence in the 2-3-year periodic band was found.

Conclusions: A multi-annual mode of oscillation was observed and these 2-3-year waves of infection probably started outside Binh Thuan province. Associations with climatic variables were observed with dengue incidence. Here, we have provided insight in dengue population transmission dynamics over the past 14.5 years. Further studies on an extensive time series dataset are needed to test the hypothesis that epidemics emanate from larger cities in southern Vietnam.

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Related in: MedlinePlus

Phase differences from Phan Thiet district.(A) Map of Vietnam (B) Mean phase differences for 1996–2001 data at the 2–3-year period band. (C) Mean phase differences for 1995–2002 data at the 1-year period band. (D) as in C, but for 2004–2008 data.
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pntd-0000747-g003: Phase differences from Phan Thiet district.(A) Map of Vietnam (B) Mean phase differences for 1996–2001 data at the 2–3-year period band. (C) Mean phase differences for 1995–2002 data at the 1-year period band. (D) as in C, but for 2004–2008 data.

Mentions: Spatio-temporal patterns were investigated by calculating phase differences as published previously [15]. Based on the results in Figure 2M, phase differences were calculated for three periods: between 1996 and 2001, when the 2–3-year periodic band was pronounced; from 1995 to 2002 and from 2004 to 2008, when the annual periodic band was significant. The average phase difference relative to Phan Thiet is shown in Figure 3. Data indicate that the multi-annual (2–3-year period band) wave of dengue infection was moving away from another epicenter, rather than from Phan Thiet district as only three districts lagged behind (negative phase difference) or the time delay was greater than a half cycle. In contrast, the annual wave of dengue infection was either synchronous (1995–2002) with all districts or moving away (2004–2008) from Phan Thiet district.


Dengue dynamics in Binh Thuan province, southern Vietnam: periodicity, synchronicity and climate variability.

Thai KT, Cazelles B, Nguyen NV, Vo LT, Boni MF, Farrar J, Simmons CP, van Doorn HR, de Vries PJ - PLoS Negl Trop Dis (2010)

Phase differences from Phan Thiet district.(A) Map of Vietnam (B) Mean phase differences for 1996–2001 data at the 2–3-year period band. (C) Mean phase differences for 1995–2002 data at the 1-year period band. (D) as in C, but for 2004–2008 data.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2903474&req=5

pntd-0000747-g003: Phase differences from Phan Thiet district.(A) Map of Vietnam (B) Mean phase differences for 1996–2001 data at the 2–3-year period band. (C) Mean phase differences for 1995–2002 data at the 1-year period band. (D) as in C, but for 2004–2008 data.
Mentions: Spatio-temporal patterns were investigated by calculating phase differences as published previously [15]. Based on the results in Figure 2M, phase differences were calculated for three periods: between 1996 and 2001, when the 2–3-year periodic band was pronounced; from 1995 to 2002 and from 2004 to 2008, when the annual periodic band was significant. The average phase difference relative to Phan Thiet is shown in Figure 3. Data indicate that the multi-annual (2–3-year period band) wave of dengue infection was moving away from another epicenter, rather than from Phan Thiet district as only three districts lagged behind (negative phase difference) or the time delay was greater than a half cycle. In contrast, the annual wave of dengue infection was either synchronous (1995–2002) with all districts or moving away (2004–2008) from Phan Thiet district.

Bottom Line: The 2-3-year periodic wave was moving towards, rather than away from Phan Thiet district.A multi-annual mode of oscillation was observed and these 2-3-year waves of infection probably started outside Binh Thuan province.Further studies on an extensive time series dataset are needed to test the hypothesis that epidemics emanate from larger cities in southern Vietnam.

View Article: PubMed Central - PubMed

Affiliation: Division of Infectious Diseases, Tropical Medicine and AIDS, Academic Medical Center, Amsterdam, The Netherlands. khoat@oucru.org

ABSTRACT

Background: Dengue is a major global public health problem with increasing incidence and geographic spread. The epidemiology is complex with long inter-epidemic intervals and endemic with seasonal fluctuations. This study was initiated to investigate dengue transmission dynamics in Binh Thuan province, southern Vietnam.

Methodology: Wavelet analyses were performed on time series of monthly notified dengue cases from January 1994 to June 2009 (i) to detect and quantify dengue periodicity, (ii) to describe synchrony patterns in both time and space, (iii) to investigate the spatio-temporal waves and (iv) to associate the relationship between dengue incidence and El Niño-Southern Oscillation (ENSO) indices in Binh Thuan province, southern Vietnam.

Principal findings: We demonstrate a continuous annual mode of oscillation and a multi-annual cycle of around 2-3-years was solely observed from 1996-2001. Synchrony in time and between districts was detected for both the annual and 2-3-year cycle. Phase differences used to describe the spatio-temporal patterns suggested that the seasonal wave of infection was either synchronous among all districts or moving away from Phan Thiet district. The 2-3-year periodic wave was moving towards, rather than away from Phan Thiet district. A strong non-stationary association between ENSO indices and climate variables with dengue incidence in the 2-3-year periodic band was found.

Conclusions: A multi-annual mode of oscillation was observed and these 2-3-year waves of infection probably started outside Binh Thuan province. Associations with climatic variables were observed with dengue incidence. Here, we have provided insight in dengue population transmission dynamics over the past 14.5 years. Further studies on an extensive time series dataset are needed to test the hypothesis that epidemics emanate from larger cities in southern Vietnam.

Show MeSH
Related in: MedlinePlus