The number of dengue cases in Singapore this year fell from the relatively high numbers at the beginning of the year.
Good news--my kids are over there right now.
Good news--my kids are over there right now.
Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).
Showing posts with label dengue. Show all posts
Showing posts with label dengue. Show all posts
Friday, December 30, 2016
Thursday, April 14, 2016
Dengue breaks out, and cools in Singapore
Last year was a relatively quiet year for dengue fever in Singapore, after the rather active years of 2013 and 2014. Ocean cooling may have been one factor, allowing the authorities anti-mosquito campaigns to make a little headway.
Late last year, the numbers began to increase, with a peak being hit early this year.
This year's initial peak is higher than any other in our data series, causing the Singaporean government to forecast in excess of 30,000 cases for 2016.
The general consensus on the cause of the spike in dengue cases has been the recent El Niño event, which normally elevates temperatures in the equatorial Pacific. By some accounts, this event has been one of the strongest on record (at least going by elevated temperatures). By some measures, the 1997-8 event was stronger. Now that the El Niño seems to be weakening, temperatures and the number of dengue cases should fall, at least until the normal seasonal warming period starts.
El Niño usually leads to warming in the Pacific ocean, with increased precipitation in the east, and reduced precipitation in the west. However, individual events have their own characteristics, and this last event differs from previous events in magnitude of warming in the central Pacific, the general lack of enhanced precipitation in western North America. Dengue outbreaks in the Phillipines and in Taiwan in late 2015 were blamed on the current El Niño event (Wendel, 2015).
Clusters of dengue cases are primarily in the eastern part of the island. Data from here, accessed on April 12.
Many of the clusters appear to be at the edges of recently developed land. These lands are those that are expected to be most marginal (i.e., low-lying, wet) and represent good breeding grounds for mosquitos. These lands have been developed recently to accommodate the rapid growth in population over the past sixteen years (according to the Singapore Department of Statistics, population has risen from 4.0 million in 2000 to over 5.5 million in 2016).
Comparison of Google Earth imagery over the past fifteen years in some of the clusters may provide some insight into the relationship between development, land use, and dengue clusters.
First up--Pas Siris. I chose this area as this is where I stayed with my family the last time I was in Singapore (just over three years ago).
Both images cover Pasir Ris and part of Tampines. The upper image was captured on February 8, 2005, and the lower image on February 25, 2015. The three transparent yellow polygons on the lower image represent identified dengue clusters as of April 12, 2016.
There has been some development during the ten years between the two images. But the most important development happened in the area beginning in 1983, before which the area was a low-lying area punctuated by small villages and kampongs.
Unfortunately, the area is so ordinary (cookie cutter buildings), that the only photos I can find of the place were of parakeets hiding in a tree outside my window at night.
One area where dengue clusters seem particularly abundant is Serangoon.
The top image is as the neighbourhood looked in 2008, whereas the lower image is the current imagery over the same area, with dengue clusters (as of April 12, 2016) superimposed on the image. If you were to locate the imagery next week or next month, you will probably find the clusters will have moved, but you will still find plenty in the area.
Very little development has occurred in the interim between the two pictures. The area is another low-lying area (although this is pretty common in Singapore). The name of the neighbourhood is proposed to have come from the name of a bird common to the swamps of the area. There are still a number of green spaces in the area, so perhaps there is a problem with local drainage.
If I were to change anything about my original thesis, that the dengue outbreaks combined natural warming with recent development of marginal (swampy) land in order to settle large numbers of immigrants, it would be to remove the word "recent". Most of Singapore was swampy, and swampy is as swampy does.
References:
Wendel, J., 2015. Dengue fever epidemics linked with El Nino, study says. Eos, 96, doi: 10.1029/2015EO037169. Published October 9, 2015.
Late last year, the numbers began to increase, with a peak being hit early this year.
This year's initial peak is higher than any other in our data series, causing the Singaporean government to forecast in excess of 30,000 cases for 2016.
The general consensus on the cause of the spike in dengue cases has been the recent El Niño event, which normally elevates temperatures in the equatorial Pacific. By some accounts, this event has been one of the strongest on record (at least going by elevated temperatures). By some measures, the 1997-8 event was stronger. Now that the El Niño seems to be weakening, temperatures and the number of dengue cases should fall, at least until the normal seasonal warming period starts.
El Niño usually leads to warming in the Pacific ocean, with increased precipitation in the east, and reduced precipitation in the west. However, individual events have their own characteristics, and this last event differs from previous events in magnitude of warming in the central Pacific, the general lack of enhanced precipitation in western North America. Dengue outbreaks in the Phillipines and in Taiwan in late 2015 were blamed on the current El Niño event (Wendel, 2015).
Clusters of dengue cases are primarily in the eastern part of the island. Data from here, accessed on April 12.
Many of the clusters appear to be at the edges of recently developed land. These lands are those that are expected to be most marginal (i.e., low-lying, wet) and represent good breeding grounds for mosquitos. These lands have been developed recently to accommodate the rapid growth in population over the past sixteen years (according to the Singapore Department of Statistics, population has risen from 4.0 million in 2000 to over 5.5 million in 2016).
Comparison of Google Earth imagery over the past fifteen years in some of the clusters may provide some insight into the relationship between development, land use, and dengue clusters.
First up--Pas Siris. I chose this area as this is where I stayed with my family the last time I was in Singapore (just over three years ago).
Both images cover Pasir Ris and part of Tampines. The upper image was captured on February 8, 2005, and the lower image on February 25, 2015. The three transparent yellow polygons on the lower image represent identified dengue clusters as of April 12, 2016.
There has been some development during the ten years between the two images. But the most important development happened in the area beginning in 1983, before which the area was a low-lying area punctuated by small villages and kampongs.
Unfortunately, the area is so ordinary (cookie cutter buildings), that the only photos I can find of the place were of parakeets hiding in a tree outside my window at night.
One area where dengue clusters seem particularly abundant is Serangoon.
The top image is as the neighbourhood looked in 2008, whereas the lower image is the current imagery over the same area, with dengue clusters (as of April 12, 2016) superimposed on the image. If you were to locate the imagery next week or next month, you will probably find the clusters will have moved, but you will still find plenty in the area.
Very little development has occurred in the interim between the two pictures. The area is another low-lying area (although this is pretty common in Singapore). The name of the neighbourhood is proposed to have come from the name of a bird common to the swamps of the area. There are still a number of green spaces in the area, so perhaps there is a problem with local drainage.
If I were to change anything about my original thesis, that the dengue outbreaks combined natural warming with recent development of marginal (swampy) land in order to settle large numbers of immigrants, it would be to remove the word "recent". Most of Singapore was swampy, and swampy is as swampy does.
References:
Wendel, J., 2015. Dengue fever epidemics linked with El Nino, study says. Eos, 96, doi: 10.1029/2015EO037169. Published October 9, 2015.
Tuesday, October 21, 2014
The peak of dengue cases for 2014 in Singapore has passed
. . . but the residual numbers of cases still greatly exceed what we observed only two years ago (data from here).
Overall, it looks like the total cases this year will be a little lower than last year, but still much higher than in 2011 and 2012.
Apart from the main peak starting and finishing a few weeks earlier than last year, I see nothing to change the following conclusion (from here).
Overall, it looks like the total cases this year will be a little lower than last year, but still much higher than in 2011 and 2012.
Apart from the main peak starting and finishing a few weeks earlier than last year, I see nothing to change the following conclusion (from here).
The increasing incidence of dengue in Singapore looks to be a reflection of government policy, which requires greater numbers of people to be stationed in close contact with mosquitos. And given that the Singapore government is pushing to increase the population by another million or so, we can only expect the trend of dengue infections to increase.
Monday, July 7, 2014
Quickie update on dengue in Singapore
After a slow start to the year, the dengue numbers have really taken off this year.
The most current information available on the status of the Pacific Decadal Oscillation suggests it is higher (warmer) than last year, which should facilitate an increase in dengue cases over last year.
Keep swatting!
The most current information available on the status of the Pacific Decadal Oscillation suggests it is higher (warmer) than last year, which should facilitate an increase in dengue cases over last year.
Keep swatting!
Friday, January 17, 2014
Cycles of dengue in Singapore
The last time I posted on this, the numbers afflicted were in decline, during the the normal seasonal drop-off. I assumed the number of cases would return to about 100 per week.
I am a little surprised to find that the outbreak is still raging. The rate of new cases is running at more than double this time last year, which was already a record. At first glance it looks like something new might be happening.
Only three years of records is too short to support such a hypothesis. Can we do better?
Although there is some agreement between the curves, particularly over the last 20 years, the small peak in the early 1990s corresponds with generally cooler surface temperatures--and the incidence of dengue was very low during the warm spell from the late 70s through to the 1980s.
One factor may be overturn of the strain of dengue encountered--for instance, the dominant strain in 2007 was different than that of 2005 (pdf). The strain in 2005 was similarly different from the dominant strain previously.
But I think the major factor in the general increase is the changing culture in Singapore. Look at the population growth of the place.
Despite only producing 1.2 babies per woman, the population of Singapore has grown by over a million in the last seven years. Obviously, this has been through immigration.
Singaporeans will no doubt complain that these newcomers don't share their cultural values--in particular, their cultural values regarding cleanliness and public order. I know, I married one. In Singaporean culture, the vacuum cleaner is not a labour-saving device, it is a device that allows you to use the same amount of labour to make the house cleaner than before.
When we were there last year, we stayed with one of my wife's relatives. They were having troubles with their new neighbours, who had recently immigrated from China, and were in the habit of tossing used diapers and tampons off their balcony.
But the reason may be more basic than that.
That snaking body of water near the top of the image is the straits of Johor, which separates Singapore from Malaysia.
Singapore is a small place. To cram in more people requires dense construction in increasingly marginal lands, which are mainly in the north and western portions of the island, and on reclaimed land, which is primarily on the southern margin. Common to all of these marginal lands is that they tend to be wet and low-lying.
The population graph has a notably higher slope (population growth) starting in the late 1980s. I assume this is the beginnings of the major influx of immigrants. Also note that this period correlates to the interval where dengue fever outbreaks begin on the chart of dengue vs the PDO. Even though conditions at the time favoured cooling, if you bring in a lot of people (a few of whom have dengue) and place them in mosquito-infested swampland, you soon have a lot of people with dengue.
The increasing incidence of dengue in Singapore looks to be a reflection of government policy, which requires greater numbers of people to be stationed in close contact with mosquitos. And given that the Singapore government is pushing to increase the population by another million or so, we can only expect the trend of dengue infections to increase.
Weekly dengue cases in Singapore, 2011-2014. Adapted from here.
I am a little surprised to find that the outbreak is still raging. The rate of new cases is running at more than double this time last year, which was already a record. At first glance it looks like something new might be happening.
Only three years of records is too short to support such a hypothesis. Can we do better?
Dengue in Singapore, 1966-2005. DHF - Dengue hemorrhagic fever;
DF - Dengue fever (only reported from 1977). Screen cap from here.
Given the population of Singapore in 2005 (4.4 million), the number of cases per 100k would give us an estimate of 14,300 cases that year. The number of cases of dengue reported in 2013 was over 22,000, and given the population estimated to be about 5.4 million, that would equate to over 400 cases per 100,000, which would be off the top of the above graph.
There are two things we note on the above graph: first is the extreme variability of the numbers of cases of dengue fever over a cycle length of approximately 8 years; secondly, the incidence of cases appears to be increasing since the late 1980s. The cycle lows are generally before 1985, around 1993, 2000, and (from the recent data) perhaps around 2011.
When I see cyclicity in epidemiological data, I look for climate oscillations. For the Pacific, we have the Pacific decadal oscillation (PDO), which alternately warms and cools the western Pacific (and many other areas, as well as changing the distribution of rainfall).
Schematic of PDO and effects on sea surface temperature from here.
During the positive phase of the PDO, we see the sea surface temperature around Singapore is a little warmer than usual. A common epidemiological argument is that warmer temperatures favour mosquitos, so if the PDO is influencing dengue cases, then we would expect to see more cases during the positive phase, and fewer cases during the negative phase. So let's combine the record from 1966 with the PDO oscillations over the same interval.
Although there is some agreement between the curves, particularly over the last 20 years, the small peak in the early 1990s corresponds with generally cooler surface temperatures--and the incidence of dengue was very low during the warm spell from the late 70s through to the 1980s.
One factor may be overturn of the strain of dengue encountered--for instance, the dominant strain in 2007 was different than that of 2005 (pdf). The strain in 2005 was similarly different from the dominant strain previously.
But I think the major factor in the general increase is the changing culture in Singapore. Look at the population growth of the place.
A snip from Google.
Despite only producing 1.2 babies per woman, the population of Singapore has grown by over a million in the last seven years. Obviously, this has been through immigration.
Singaporeans will no doubt complain that these newcomers don't share their cultural values--in particular, their cultural values regarding cleanliness and public order. I know, I married one. In Singaporean culture, the vacuum cleaner is not a labour-saving device, it is a device that allows you to use the same amount of labour to make the house cleaner than before.
When we were there last year, we stayed with one of my wife's relatives. They were having troubles with their new neighbours, who had recently immigrated from China, and were in the habit of tossing used diapers and tampons off their balcony.
But the reason may be more basic than that.
Image of Singapore.
That snaking body of water near the top of the image is the straits of Johor, which separates Singapore from Malaysia.
Singapore is a small place. To cram in more people requires dense construction in increasingly marginal lands, which are mainly in the north and western portions of the island, and on reclaimed land, which is primarily on the southern margin. Common to all of these marginal lands is that they tend to be wet and low-lying.
The population graph has a notably higher slope (population growth) starting in the late 1980s. I assume this is the beginnings of the major influx of immigrants. Also note that this period correlates to the interval where dengue fever outbreaks begin on the chart of dengue vs the PDO. Even though conditions at the time favoured cooling, if you bring in a lot of people (a few of whom have dengue) and place them in mosquito-infested swampland, you soon have a lot of people with dengue.
The increasing incidence of dengue in Singapore looks to be a reflection of government policy, which requires greater numbers of people to be stationed in close contact with mosquitos. And given that the Singapore government is pushing to increase the population by another million or so, we can only expect the trend of dengue infections to increase.
Tuesday, July 23, 2013
Update on dengue in Singapore
After peaking in late June, the number of cases has fallen by more than half, to about 340 last week. Total number of cases this year is about 13,500.
Friday, June 14, 2013
Singapore faces worst dengue fever outbreak in its history (updated)
On our last trip to Singapore, my wife insisted that the mosquitoes there were not a concern. This is no longer the case. Singapore is in the throes of its worst outbreak of dengue fever ever. No explanation has been offered for the size of the outbreak, although there have been comments that the virus has a greater resistance to treatment than normal.
I'm not convinced--in my experience with tropical disease outbreaks in Africa and other places, it is almost always caused by higher than normal rainfall. In Singapore it may be compounded by the large number of construction projects underway.
Dengue is caused by a virus which is spread by mosquitoes. There is no vaccine, so you avoid dengue by avoiding mosquito bites.
Last year Singapore experienced a little over 4,500 cases of dengue fever (which seems like an awful lot to me). That would be less than one case per thousand population. This year, the number is already over 10,000, with over 800 new cases this week alone. They have not yet reached the time of year where the number of cases normally peaks. There have been two deaths.
It's hard to make sense of the distribution of cases. The Paisir Ris cluster is an area of apartment blocks, but there is a lot of green space between the buildings and a fairly large series of connected parks.
Downtown shots, not Pasir Ris. Couldn't find any good shots of Pasir Ris except inside the apartment.
Updated June 26
Numbers still growing, with the peak still likely a few weeks away. Graphics source.
I'm not convinced--in my experience with tropical disease outbreaks in Africa and other places, it is almost always caused by higher than normal rainfall. In Singapore it may be compounded by the large number of construction projects underway.
Dengue is caused by a virus which is spread by mosquitoes. There is no vaccine, so you avoid dengue by avoiding mosquito bites.
Last year Singapore experienced a little over 4,500 cases of dengue fever (which seems like an awful lot to me). That would be less than one case per thousand population. This year, the number is already over 10,000, with over 800 new cases this week alone. They have not yet reached the time of year where the number of cases normally peaks. There have been two deaths.
Dengue cases this year. From here.
It's hard to make sense of the distribution of cases. The Paisir Ris cluster is an area of apartment blocks, but there is a lot of green space between the buildings and a fairly large series of connected parks.
Downtown shots, not Pasir Ris. Couldn't find any good shots of Pasir Ris except inside the apartment.
Updated June 26
Numbers still growing, with the peak still likely a few weeks away. Graphics source.
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