Dengue Sri Lanka; 2015 -2020

The nations of the world are in the grip off the COVID 19 pandemic but that doesn’t mean that we should forget about Dengue Fever! 2017 was a terrible year and one which showed quite clearly that the authorities did not have a grip on the disease. While 2018 saw a small reduction in cases in 2019 cases rocketed once more.

• Number of recorded case
• 2015               29777
• 2016               55150
• 2017             186101
• 2018               51659
• 2019             105049
• 2020              22,390 to end of June

 

So far,  in 2020 the number of registered new cases is much lower than for previous years. The question is why? Is it just that during the lockdown new cases were not reported? Or is it the result of people staying indoors and either not getting bitten by the mosquito or not passing  the virus on?

Originally this post charted the development and spread of the virus through 2018. Instead of repeating that exercise we are going to be looking at the evolution of the disease over a 5 year period including the epidemic year, 2017. 

Using the administrative districts map as the reference point and the calculating the number of cases per month per 1000 of the population we can analyse the  patterns that emerge, not just in terms of where dengue cases are recorded, but also at what times of the year.

note; cases per 000 gives a much more accurate picture of prevalence within a district than total number of cases, although the latter is useful for estimating where the peak demand for hospital beds will be.

The Administrative Districts

Sri Lanka Administrative districts

Cases per 100,000 of the population by administrative district

Census 2012	Population	2015	2016	2017	2018	2019
Colombo	2,324,349	4.25	7.21	14.9	4.41	8.7
Gampaha	2,304,833	1.80	3.11	13.7	2.49	6.8
Kalutara	1,221,948	0.78	2.89	9.0	2.53	6.5
Kandy	1,375,382	0.96	2.95	10.7	2.78	6.4
Matale	484531	1.21	2.37	6.5	1.87	4.8
Nuwara Eliya	711644	0.25	0.59	1.3	0.29	0.6
Galle	1,063,334	0.97	2.90	6.0	0.90	6.5
Hambantota	599903	0.66	1.50	6.0	1.82	3.3
Matara	814048	0.56	1.70	7.8	1.40	4.9
Jaffna	583882	3.45	4.23	10.4	6.95	13.5
Kilinochchi	113510	0.81	0.76	5.0	3.02	3.3
Mannar	99570	1.05	2.32	5.4	2.20	2.4
Vavuniya	172115	1.15	1.56	6.2	3.42	4.7
Mulativu	92238	1.54	1.98	4.2	1.23	2.6
Batticaloa	526,567	2.80	1.16	10.6	9.19	4.8
Ampara	649402	0.10	0.40	1.4	0.36	0.6
Trincomalee	379541	1.54	0.95	13.2	2.94	6.9
Kurunegala	1,818,465	0.70	1.41	6.2	1.34	1.7
Puttalam	762396	0.97	1.38	10.3	2.64	2.8
Anuradhapura	860575	0.47	0.85	3.4	1.00	1.3
Polonnaruwa	406088	0.62	1.18	3.5	0.79	1.3
Badulla	815405	0.69	1.45	4.5	0.75	2.3
Moneragala	451058	0.49	1.05	7.2	1.89	0.7
Ratnapura	1,088,007	0.96	2.88	10.4	2.04	3.6
Kegalle	840648	0.85	1.80	11.4	1.82	3.2
Kalmunai	106780	5.08	9.15	28.4	16.47	12.9
average	21,413,249	1.39	2.58	8.69	2.41	4.91

Emerging Patterns

1. 5 towns have above average cases per 100,000 in all 5 years; Colombo Gampaha, Kalmunai and Jaffna.
2. 3 towns have 4 years above average; Kalutara Kandy and Tricomalee
3.  Batticaloa was above average for 3 of the 5 years
4. Galle Puttalam and Ratnapura were above average on two of the years

These centres seem to be the recurring hubs of infection.

• By far the highest prevalence is found in Kalmunai; around 3+ times the national average in all years.
• While Colombo was similar in comparison to  the national average in 2015 by 2019 that had reduced to around twice the national average.
• Jaffna shows a worrying rising trend in terms of prevalence; and seems to be going the opposite way to Colombo.
• Data for Kandy shows an upswing in cases per100,000; something that is mirrored to a degree in the data for the first half on 2020.
• Both Tricomalee and Batticaloa have experienced two surges of infection.
• 2017 was an epidemic year but even then the largest number of infections was confined to Western Province, Kandy, Batticaloa and Trincomalee, Kalmunai and Jaffna. Other districts escaped relatively unscathed; why?

So the data throws up questions:

1. Why is the prevalence of dengue so high in Kalmunai when Ampara as a whole has so few cases?
2. Why are cases in Gampaha so much lower than Colombo? After all both are similar climate wise?
3. Why is the number of cases in Jaffna rising inexorably?
4. What is going on in Trincomalee and Batticaloa which might account for the increase in prevalence?
5. The same question applies to Kandy.

Nearly always the reason for an increase in cases is failure to control the mosquito vector. And a number of reasons have been advanced in the recent past to explain the data.

• tourist deposited trash has been blamed for the rise in cases in Kandy; (the garbage left in the streets being ideal breeding grounds for the mosquito)
• failure to control or manage building sites in Batticaloa leaving mosquitos to breed in secluded corners etc has also been cited
• inadequate water storage in poorer districts in Jaffna has been mentioned
• how has population movements between districts changed especially since the end of the Civil War? Is there any mileage in looking at patterns of trade and people movements between the districts and Colombo for example to see if there is any correlation between contact with Colombo and increased cases?
• But what is it about Kalmunai? Why has so little apparently been done to change the situation?

…and so on.

However, the evidence is circumstantial at best. It is about time some more detailed collection of evidence was undertaken to see whether there is a correlation between the opening up of building sites and an increased number of cases, for example.