Where is the Mosquito — HK Dengue Fever Frontline Part 3: Visualising Ovitrap Index

This is the third post of the independence project, finding which area has the highest Ovitrap Index in Hong Kong. For anyone who is interested in the data used in this post, you are welcome to read the Part 1: Data Cleaning and Part 2: Create a SQLite database of this project.

After cleaning the data and put them into the database, it is finally the time to explore which area has the highest Ovitrap Index in Hong Kong. Just a friendly recap, Ovitrap Index is used by the Hong Kong Food and Hygiene Department (FEHD) to understand the extensiveness of the distribution of Aedine Mosquito, which is capable of spreading a common but dangerous disease ‘Dengue Fever’ in South East Asia, in the selected area. This Area Ovitrap Index (AOI) allows us to find out which area needs more mosquito control even though a higher AOI does not mean that there must be Dengue Fever. As the data collection process is in the early August 2018, the data used is from January 2008 to July 2018. The FEHD website has been changed after August, AOI is collected in two phases and will be shown on the website with the calculated average starting from September 2018. However, as this project is using data before the change, this analysis is not affected.

Let’s look at a bigger picture first. According to the FEHK division, there are total 19 districts in Hong Kong (For any confusing HongKonger, yes, there are 19 districts in this case). Although some districts have more Ovitrap locations, it is more consistent and logical to follow the division of FEHD.

The Yearly Ovitrap Index of every district is calculated by summing the Yearly Ovitrap Index of locations which are in the same district and divided the sum by the number of locations in that district. For example, WanChai District has three locations: Tin Hau, Wan Chai North, and Happy Valley. The Yearly Ovitrap Index of these three locations are calculated and summed, then the sum is divided by 3, which is the number of locations in the WanChai District.

SQL is useful to not only extract the needed data from the database, but it also supports the calculation efficiently.

“?” after “LIKE” is a placeholder which represents the years from 2008 to 2017

A dataframe is then created to stored these extracted data.

Now we can start answering questions like:

Does there any district continuously has a higher AOI from 2008 to 2017?

Top three districts in each year. Black means highest Ovitrap Index, followed by red, and orange.

This bar chart tells us the Yearly Ovitrap Index of each district from 2008 to 2017. As we want to know which district has a higher Ovitrap Index than others, the top three districts of each year are coloured. Higher the Ovitrap Index is, darker it is. The winner is in black and the second runner-up is in orange. We can see that the differences between the top three districts are not always that much. However, it seems that some districts have been coloured more than others.

Let’s make a simple counter to check whether it is true.

Districts that have never been top three are not in the Counter

Kwun Tong District was in the top three in 9 out of 10 years, but Kwun Tong District covers several locations. Before deciding whether the whole district needs more mosquito control, it is better to take a closer look at the district.

Only the highest and lowest Ovitrap Index are presented because the differences between each location are already clearly shown.

There are three locations in Kwun Tong District from 2008 to 2017. Kwun Tong Central has a higher Ovitrap Index than Lam Tin except 2008 and 2014. While Kowloon Bay was only available after 2014, Kwun Tong Central is very likely the reason why Kwun Tong District has higher Ovitrap Index before 2015. Also, it is worrying that the Ovitrap Index of Kowloon Bay increased rapidly and greatly exceeded Kwun Tong Central in last year.

We now know that the Ovitrap Index of Kwun Tong District has been quite high in the last 10 years, let’s see its performance from Jan 2018 to Jul 2018.

All districts are shown in this line plot

Although it has not reached the highest index (the 27.6% of North District), it keeps rising and become the highest in July this year. It is clear that there should be stricter mosquito control in Kwun Tong District. Before closing the case, let’s consider one more question.

According to the Center for Health Protection, most of the cases of Dengue Fever in this summer were in Wong Tai Sin (Wong Tai Sin District) and Cheung Chau (Islands District). As what we can see from the line plot below, a high Ovitrap Index does not always lead to an outbreak of Dengue Fever, but the underlying risk of an area having high Ovitrap Index should not be neglected.

While Wong Tai Sin is geographically close to Kwun Tong, if the outbreak of Dengue Fever in Wong Tai Sin spreads to Kwun Tong, which has high Ovitrap Index in these years, it can be very worrying. Although it does not seem to be happening, it is not wrong to play a safe card. To prepare for this worrying combination, let’s look closer into both districts:

From the above line plot, Wong Tin Sin Central and Kowloon Bay should be considered as the first priority to have a stricter mosquito control. As what has discussed above, Kowloon Bay maintains its momentum from the previous year but Kwun Tong Central seems to be under controlled. However, you may notice that the red dot on the right line plot representing Yau Tong has a terrifying AOI. It is only recorded after June 2018, so it is possible that the mosquito control in there was less than others. It is believed that Yau Tong is not the only case, therefore, to have a more comprehensive understanding of the extensiveness of Aedine Mosquito in Hong Kong, more area should be under the monitor of Ovitrap.

As there are many factors that may lead to an outbreak of Dengue Fever in an area, Ovitrap Index is only one of the useful monitoring tools. However, if the Ovitrap Index can be used effectively, the mosquito control can be conducted in a more efficient way.

Thanks for reading. This is the last part of my first independent project. This time, we have found locations that need more and stricter mosquito control. Although there are many explorations that are not covered, I hope this project can also tell you why Ovitrap Index and monitoring the Aedine Mosquito are important. For anyone who is interested in the full code, you are welcome to visit this Github. Also, if anyone has any comment, I am very welcome to listen to and learn from it :)