Limits...
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.

Show MeSH

Related in: MedlinePlus

Wavelet coherence and phase analyses of dengue time series between neighboring districts in Binh Thuan province.The left panel represents the wavelet coherence. Blue, low coherence; red, high coherence. The dotted lines show α = 5% significance level. The cone of influence (black curve) indicates the region not influenced by edge effects. The right panels represent the phase analyses between two districts (in blue and red), based on wavelets for 2–3-year periodic band. Green boxes represents the period of time where coherency is significant, when interpretation of analysis was possible. Red lines: first district; blue lines: second district; dashed black lines: phase difference between the two oscillating components.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2903474&req=5

pntd-0000747-g002: Wavelet coherence and phase analyses of dengue time series between neighboring districts in Binh Thuan province.The left panel represents the wavelet coherence. Blue, low coherence; red, high coherence. The dotted lines show α = 5% significance level. The cone of influence (black curve) indicates the region not influenced by edge effects. The right panels represent the phase analyses between two districts (in blue and red), based on wavelets for 2–3-year periodic band. Green boxes represents the period of time where coherency is significant, when interpretation of analysis was possible. Red lines: first district; blue lines: second district; dashed black lines: phase difference between the two oscillating components.

Mentions: We compared dengue dynamics between neighboring districts when periodicities were detected in each district (Figure 2-A to L). High coherencies in all comparisons were detected for the 1-year periodicity (left). This annual mode of oscillations was also observed in the phase angle analyses (see Figure S2). Multi-annual oscillations at a 2–3-year period were identified, although these oscillations were transient and varied in time and space. There was a tendency that the multi-annual oscillation returned after 2006. Globally, coherency analysis between dengue incidence time series in Phan Thiet district and the eight other districts together shows two main regions of high significant coherence (Figure 2M). The first one is for the 1 year periodic band in 1995–2003 and in 2004–2008 and the second is for the 2–3-years bands in 1996–2001. Although there is a third significant coherence region (4 year periodic band, 2003–2004), it must be interpreted with caution due to the short length of the time series.


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)

Wavelet coherence and phase analyses of dengue time series between neighboring districts in Binh Thuan province.The left panel represents the wavelet coherence. Blue, low coherence; red, high coherence. The dotted lines show α = 5% significance level. The cone of influence (black curve) indicates the region not influenced by edge effects. The right panels represent the phase analyses between two districts (in blue and red), based on wavelets for 2–3-year periodic band. Green boxes represents the period of time where coherency is significant, when interpretation of analysis was possible. Red lines: first district; blue lines: second district; dashed black lines: phase difference between the two oscillating components.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0000747-g002: Wavelet coherence and phase analyses of dengue time series between neighboring districts in Binh Thuan province.The left panel represents the wavelet coherence. Blue, low coherence; red, high coherence. The dotted lines show α = 5% significance level. The cone of influence (black curve) indicates the region not influenced by edge effects. The right panels represent the phase analyses between two districts (in blue and red), based on wavelets for 2–3-year periodic band. Green boxes represents the period of time where coherency is significant, when interpretation of analysis was possible. Red lines: first district; blue lines: second district; dashed black lines: phase difference between the two oscillating components.
Mentions: We compared dengue dynamics between neighboring districts when periodicities were detected in each district (Figure 2-A to L). High coherencies in all comparisons were detected for the 1-year periodicity (left). This annual mode of oscillations was also observed in the phase angle analyses (see Figure S2). Multi-annual oscillations at a 2–3-year period were identified, although these oscillations were transient and varied in time and space. There was a tendency that the multi-annual oscillation returned after 2006. Globally, coherency analysis between dengue incidence time series in Phan Thiet district and the eight other districts together shows two main regions of high significant coherence (Figure 2M). The first one is for the 1 year periodic band in 1995–2003 and in 2004–2008 and the second is for the 2–3-years bands in 1996–2001. Although there is a third significant coherence region (4 year periodic band, 2003–2004), it must be interpreted with caution due to the short length of the time series.

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