Mapping the Dengue Cases Distribution with Google Earth Pro™, Geocoding Attributes Tables

Abstract

When the epidemiologists need to analyze the distribution of cases in a study or the outbreak trend of cases over time, usually they use graphics for representing the magnitude over time (by incidence and prevalence), tables for describing the variables of the affected people (by race, age, sex, weight, and social condition), and maps describing the spread of places and distribution over time. The technological advances gives most people access to latitude and longitude in smartphones and easy access to a GIS-like free software such as Google Earth™ (GE), an intuitive and effective program for a fast map of the case addresses geocoded, an easy way to display layers imported from formats like Shapefiles extension, and showing over those layers Excel tables with the patient variables and geocoded data from the sheet. Besides, it gives the availability of saving the spatial data with the variables, in files that can be mailed and displayed in smartphones and PCs with Google Earth installed and with outcomes that have a format compatible to GIS classic software.

1. Introduction

Geographic information systems (GISs) are commonly used by professionals for analysis of geocoded data over maps. But these software are for specialized and trained personnel. Some of them like Arc Gis™ are licensed and have an important economic cost; some other like Quantum Gis™ are open source but not easy to use without appropriate training; some other like EpiInfo™ allows to create variable income of cases and associate them with the geocoded data.

But Google Earth Pro™ has proven to have an extra advantage over classic GIS software. It has the possibility for searching places by typing the name while using it for mapping and also by copying the geocoded data from the search bar placemark, which appears on the surface of earth satellite imagery or the commercial sites in search. So, it is very easy to locate reference places like parks, hospitals, or buildings and approach the address of a patient’s home, and this way, the epidemiologist can make the mapping free and easy geocoding of the attribute of the table linked to the corresponding marks in the map.

In 2013, the author of this chapter worked as an epidemic surveillance professional for the government health ministry and tried to give a better representation of the affected places in a rural town, Nandayure, located in the Guanacaste region of Costa Rica, Central America. That region is one of the 3 regions from Costa Rica that usually concentrates over 80% of dengue cases among 9 regions of the public health system [1] and is endemic for dengue fever and other arthropod-borne viruses like chikungunya and Zika, but not for malaria or yellow fever.

So the author of this chapter reported the findings to the director of the office and with another office partner created an original paper of the new case of use of GE™ for mapping cases of dengue, with the combination of excel table of attributes, just like joint function in GIS classic programs but easier.

The occurrence of outbreaks motivates epidemic interventions, in order to control the spread of the viruses and to avoid more neighborhoods and other towns from getting affected. So, the map of the incidence every day or week permitted to make an analysis of the magnitude of the spread for targeting a more extensive application of insecticides [2], and this way it helped to have a lower cost and more effective control of the adult mosquitoes, near the affected person.

The incidence of arbovirus-infected patients in a medical center implicates a report ticket submission to the surveillance in 24 hours after medical assistance in Costa Rica’s health system, because this establishes sanitary legislation and regulations [3, 4], and 48 hours after ticket reception the vector control health workers must start investigation, looking for breeding sites of Aedes sp and applying insecticide in the house and surrounding houses. Mapping cases of dengue fever is important and necessary for distribution surveillance. But is not acceptable by croquis, or drawings that lack of adequate scale. Especially when everyone has access to satellite imagery free and easy with GE™.

The use of GE™ for the mapping of cases became a case study, and the advantages found in the software were important for improving the quality of representing outbreak advance and control. Because of the images that were offered by the software, it made easier it to save and compare the data over time. Intuitive interface made easy to mark a place with a click of the mouse, and right click permitted us to see the altitude, latitude, and longitude of that mark; rename, cut, and copy; change position; add an image; and so on, just like moving a file in the desktop screen of a PC. The case study becomes a case of use, when the software is commonly used for technical reports, with maps showing the satellite image quality, with title, legend, cardinal points, and scale, by only clicking on a tool bar at the bottom.

At the end of 3 years of use, the author realized that is it possible to take a mark or a group of placemarks from the layer panel, at the left side of GE screen, and convert them it into an Excel sheet, and it is possible to do the opposite: importing an excel table with typed latitudes and longitudes, having as a result a geocoded mapping of dengue patients, showing the coordinates as marks on the satellite images map of Google software. The union of these data from the Excel of attributes with the marks coordinates obtained from health care givers about infected people has an improved database in three dimensions, because it includes time space and person variables at the same time.

All data and variables like the onset of symptoms, address geocoded, and the characteristics of the persons like age, sex, name, date of birth, ID number are provided in a file .text extension that allows to import the data and show them on Google Earth. The label is chosen from the attributes table with the import procedure and with an intuitive navigation as simple as a left click and shows all the data from the patients’ information, and the imported sheet can be saved as a file easy to send as an email attachment and has been proven to be compatible with classic GIS software since 2008 [5].

And that is useful for adding a higher quality map, with marks representing data important for analyzing trends, showing the affected area on a global scale where it is possible to zoom in and out to get a satellite quality view of the streets, relief, and flora. And with great accuracy, it is very easy to get to the roof of a patient’s house just by scrolling with the mouse.

A better way for reporting the epidemic distribution of patients’ incidence, with layers that can be displayed sequential weekly or monthly, is by just saving different files according to the needs; this way the epidemiologist can explain the location where the outbreak started and how it increases and spreads, to focus efficiently on the intervention and the resources for the decision makers.

Mapping with GE™ began as a case of use for displaying marks representing sickness distribution in a satellite picture from a visor named GE and became a GIS-like layer viewer, with information about patients who had dengue fever, geocoding the houses where they live for a better epidemic surveillance, mapping and analyzing data according to the neighborhood population, altitude, temperature, and urban population density. That case of use of a free software became an original article [6].

2. Using Google Earth Pro™ (GEPro) as a geographic information system

A spot map is used to display the location of each health-related state or event that occurs in a defined place and time. With rare diseases or outbreaks, each point on the map represents a case. An area map may also be used, which indicates the number or rate of a health-related state or event by place, using different colors or shadings to represent the various levels of the disease, event, or behavior [7].

2.1 GIS + epidemiology

The spatial analysis of epidemic phenomena like uniting space, time, and person with all important variables is the backbone for public health.

The time of the year an outbreak starts is important, including when the increase of the incidence is already known previously, like seasonal flu. And weather-related conditions such as temperature, tropical rainy season, and altitude have influence over vector-transmitted diseases; dengue fever is a seasonal and environment-related incidence sickness [8].

These geographic terms are increasingly finding their way into the epidemiologic literature, as advances in the GIS technology make it ever easier to connect spatially referenced physical and social phenomena to population patterns of health, disease, and well-being. Modern geography allows us to understand the space and how its singular environment has an influence over countries, regions, and places [9]. Matching the spatial distribution of cases and outbreaks to the individual, demographic, social and geographic particularities [10].

The variables about a person and its condition are important; for example, taking care of a pregnant woman in a Zika outbreak is fundamental for avoiding congenital abnormalities; some strategies include giving nets to pregnant women [11, 12].

The unstoppable actualization of geographic information software and the free access to satellite imagery make it easier to epidemiologically apply the advantages. Besides the description or illustration of one condition, the selection of more affected areas must be the focus for the prevention plans and interventions and for the search of possible solutions to the etiology of the condition [13].

The burden of the disease, the global impact, and the vector-transmitted arbovirus become medullar for the necessary increase of the use for satellite imagery. And the advantages offered by GIS have been promoted by the World Health Organization [14] for the prevention of and attention to dengue.

Pan-American health organizations have promoted the use of GIS as a part of their projects to strengthen the capacities of the governments from North, Central, and South America [15].

Nevertheless, it is uncommon to use a GIS for the “place”-related analysis, and usually, rates of people over place are displayed like the entire geographic area in a code of colors that represents level of affection according to those rates. While some health systems in poor developing countries still have whiteboard croquis, some countries have control over the information of patients for preventing epidemics very strictly, by the use of artificial intelligence like by China during the Covid-19 pandemic. One of the experiences of the use of Google Earth for epidemic surveillance was the controlled isolation of Covid-19 infected people; many countries established quarantines and isolations, and some of them developed software for the geocoded control of the isolated people for the respect of isolations and quarantines [16].

Improving urban Aedes control and achieving a measurable impact on dengue virus transmission require a reformulation of current strategies and a stronger focus on the adult mosquitoes that actually transmit the disease, both lowering vector abundance and preventing human–vector contact [17].

In Costa Rica, surveillance of dengue includes the intradomicile and extradomicile insecticide application for the house of a person diagnosed as likely dengue or confirmed dengue, and sometimes the place of work, schools, and public institutions are also treated. There is control o larval, adult, and breeding sites.

Where a case of dengue reported stays the most duration of time, some surrounding houses are also treated, for the protection against the possible infected mosquitoes. If the person has been in medical assistance, the surveillance structure of the mandatory public health system laws and guidelines include the case report and investigation about the places visited 15 days back. And in the case of an outbreak, mapping the cases through the weeks is mandatory until the outbreak is under control [18]. But mapping is not usually as good as the high level of quality of geocoded satellite imagery as Google Earth offers.

Dengue fever is a vector-transmitted disease. Dengue transmission occurs through an insect vector, predominantly Aedes aegytpi but also Aedes albopictus. Environmental parameters, especially temperature and precipitation, affect the demography and behavior of these vectors, making dengue an obvious candidate to investigate the impact of climate on the disease [19].

In 2008, a group of epidemiologists concluded in a Bulletin of the World Health Organization about the importance of taking advantage of Google Earth uses and explained how advanced and costly concepts for disease surveillance could turn into an opportunity to apply low-cost tools and solutions. GE™ proved to be an excellent way to develop great alternatives for improving public health by the urban visualized spatial patterns of vector-borne diseases, creating maps showing the location of blocks with dengue cases reported in 2006 for Chetumal and Merida, México. They showed how to draw blocks made with polygons that would be colored for demonstrating where the cases of dengue affected that block. And they added marks for labeling infrastructure. But they described limited access then, because of limited internet access in developing countries and rural images that were of poor quality at that time. But this limitation with regard to rural imagery quality changed in 2015 after GEPro™ became free to access [20].

Now instead, the case of use becomes an advantageous technique for any user who requires the map to show the distribution of any Excel sheet on satellite imagery quality. The next is an explanation about the step-by-step process for mapping the entire Excel with attributes and the geocoded address, based on the experience of the place distribution analysis obtained after mapping for each patient reported as a case of dengue fever to the surveillance system, in a rural place from Costa Rica.

To obtain a detailed mapping with all the cases represented over the satellite image, keep all the variables originally in the sheet of the workbook. And for any Excel with geocoded data, patients’ workbook can be imported from Google Earth. A sheet with geocoded data of hospitals, or neighborhoods, or houses covered by the medical or insurance service shows the details of each variable of interest.

2.2 Is Google Earth™ an SIG?

2.2.1 Software description

The program starts with an interactive globe, and with the scrolling of the mouse, it can easily zoom in to any point on the surface of the earth, with a high level of detail and accuracy. In the program, the view shows relief; can measure routes and distances between two points; generate polygons and area measurements, circle radius, areas, circumference, and diameters; open other layers; and import other formats like shape files. The layer panel, to the left and down of the screen, lets activate roads, places, photos, announcements, 3D buildings, borders, and labels [21]. But the most important difference or advantage over classic GIS programs is the option to search for a place or direction.

GEPro™ is a layer viewer that could not be considered an authentic GIS, because some spatial analysis tools are not available, neither layer editions nor access to attribute tables. But it is becoming the key for the public health map of events [22]. Besides that, it offers high-quality satellite imagery and powerful search tools, for commercial infrastructure, public infrastructure, and places from local territorial division.

But it is not available to filter marks from a group of placemarks, for creating a new layer based on attributes, like filtering on the classic GIS layer. Hence, if a user has a layer in GE™ that shows the addresses of the dengue cases that have occurred in 1 year, it is not possible to select a filter and create a new layer with only 3 months. The way to create that filtered layer would be to filter in the Excel the 1 year table of attributes, copy in a new Excel only the information from the filter, save the Excel in a (Tab delimited)(*.txt). format, and import the new layer from the GE software.

The procedure in this chapter shows the steps of a case of use where an Excel attribute sheet is imported as a text sheet from a workbook with latitude and longitude to GEPro™. The user has access to the variable tables by clicking the placemarks; the marks can show individually the information from the original Excel attribute table when it is left clicked on the placemark.

But if you need to convert a group of marks that you obtained from GPS into an Excel file, it is possible also by another case of use of GEPro™, moving all the points or marks into a folder in the left viewer, saving as a KML file, and then converting KML into an Excel workbook.

With a right click on the left panel of places for creating a new folder, the placemarks can be moved with the left click to the folder or copied the same way a folder is created and files are moved in the screen of windows; cut and paste with a right click for the mark you will move to that folder created in the placemarks panel.

And with the same right click, save the file into a KML or KMZ format, and that file extension can be used for creating the Excel workbook with all the latitude and longitude data, very easily, by accessing the free Geodata converter on the internet [23]. Then, import the KML or KMZ file saved and convert it into an Excel workbook with coordinates.

There are 3 versions of Google Earth™: normal, Pro, and enterprise open source; all of them are free. But the one described here is Google Earth Pro™. The standard version allows comment maps and creates files KML format, placemarks, polygon, lines, routes, and show layers of maps. The Pro was designed for commercial and professional use but became freely available in 2015 and incorporated improvements about import of maps and digital layers in different formats. The Pro version allows up to 2500 marks sharing and improved the resolution for all images and maps in even rural areas (Figure 1), thus enabling the user to explore demographic data, print screen, and make movies off connection [20].

Figure 1.

A scale map of a rural neighborhood created from Google Earth Pro™. Figure created by the author of this chapter.

Google Earth frame is based on satellite imagery (Landsat, SPOT, Quickbird) and aerial photography; both of these are periodically actualized. Satellite imagery is full of quality and has great accuracy; thus, a high resolution of Google Earth Pro is guaranteed, the interval of error goes from 0.6 to 1.3 meters [24]. By the year 2016, Google Earth image resolution improved even more, due to Landsat 8th imagery [25].

Some authors indicate Google Earth is not a GIS; maybe it is not a classic one like ArcGis™ or QGis open source, but it is compatible with them because the outcome format KML can be opened on classic GIS software. And it has advantages over classic ones, because it is easy to access, reliable, fast, portable, free, and intuitive and offers powerful search.

3. Procedure concerns for mapping the Excel with geocoded addresses

3.1 Installation

First of all, one must install Google Earth Pro™ by downloading the program from the official website [26].

Once you start using it, it is very important to go to the tools, select options, and change the Show Lat/Long options, choosing decimal degrees, because the program begins when it opens the first time, showing degrees in minutes and seconds; this is a format that is not compatible with most of the cellular coordinates that often are shared by message services like WhatsApp location sharing.

3.2 Excel considerations

The second basic concern is to check the Excel workbook, which must have only one sheet, because the import of a file is only for a singular sheet. When the Excel has the latitude and longitude separated by comma, the file imported in GEPro™ will have a problem for the decimal reading; thus, the decimal must be separated by a point. For an easier and faster change, go to the search option in Excel and choose the replace option; there you have to type a comma for the search and type a point as the replace; it is going to change all the comma-separated decimal to point-separated ones (Video 1 available at: https://youtu.be/29BR7NM52XY).

3.3 Mapping patient’s address in Google Earth Pro™

Epidemiologists are daily familiarized to databases that show variables of the victims or affected cases; most of those data can be exported to other formats and there is always an Excel workbook option outcome, which contains the list of patient information like ID, date of birth, symptom onset date, sex, work, address, and more.

But if the direction is from a place the user does not know or is located in another city, or if the epidemiologist mapping that case is new in the town, the map of cases could be a big deal. In this case, the user of GEPro™ can take the address and type in the Google Earth search panel the name of the building where the person reported to be living at the moment of the medical attention or the coordinates sent from a WhatsApp message of the patient’s location.

For example, if the address is 600 meters north from the church, it is so easy to place a mark by typing the name of that church in search option, then with the rule measure, the 600 meters in the north direction guided by the cardinal points is shown on the screen. The rule is one of the most important in the tool bar, which helps to place a mark based on the address.

In the approximated measurement, the user sets the placemark and copies the coordinates of the latitude and longitude, so these values must be pasted to the latitude and longitude column in the Excel, with a negative sign in the case of western hemisphere and southern hemisphere. This way, the epidemiologist goes on to add more geocoded addresses to the Excel due to the cases.

3.4 Correcting an address

Sometimes, trying to find the house of the person with dengue fever symptoms, for the necessary breeding site assessment and insecticide intervention, can be difficult because the direction given by the person to the medical service was not good enough because of missing information, or wrong cardinal point reference, or not being the current address anymore. And the health worker can ask the patient for the coordinates of the current address by cellular phone to relocate the geocoded position of that house. That way the arbovirus assessment can be more accurate, and the change in the address of patients can be done right and easy. Just change the data of the latitude and longitude columns from the excel sheet and this way correct the wrong address and save the workbook for importing again from GE™.

An experience of isolation and control of transmitted disease with geocoded data, occurred when a tourist visited for vacations during pandemic between 2020 and 2021. Before leaving the country it was necessary a negative test for covid, but if the person tested positive to Covid-19, that tourist had to stay more days in the country for isolation, and sometimes needed to find another place to move, because the next days, the room would be reserved for other tourists, so the Covid-positive person sometimes had to change the place of isolation.

In this case, the coordination with the surveillance system may include the patient asking for permission or communicating to the professional epidemiologist of the surveillance system to move to another place. And one of the ways to confirm the new location of isolation could be by sending a mail or message to confirm the new place coordinates to continue isolation; the person can be asked if they agree to send a message with the location from the cellular phone through a WhatsApp message or email. Sending location before getting out of the room and when arriving to the next room or hotel can help the health system give better and faster assessment in the case of an emergency.

3.5 Importing data from Google Earth

The Excel workbook must have only one sheet, and for the import of the data, we have to save that workbook as a copy, in a text format that looks this way: (Tab delimited)(*.txt). That file is the one for import; in Google Earth Pro™, go to the tool bar, File/Import; there the file will be shown while selecting the generic text *.txt *.csv format that corresponds to the name of the workbook tab delimited saved.

When all the addresses are geocoded with corresponding latitude and longitude for each case in the Excel workbook, it is very important to fill all empty or missing data of the sheet with alternative words, like typing null, 9999, empty, missing, or any word that completes that missing data, because empty cells can make the display of variables misplaced, when importing the workbook from Google Earth.

3.6 Creating layers with filtered data from Excel sheet

If epidemiologists, health providers, or any user has all yearly data of dengue cases in an Excel workbook and wants to create a layer with only one-month cases of dengue, to see a one-month layer of marks, one must filter the month in Excel, copy the elements, and paste them on another workbook. And save this new workbook as a layer of cases with the only filtered month as another text sheet or (Tab delimited)(*.txt).

3.7 Opening the layer of marks in Google Earth Pro™ and final steps for the template

When importing, the user must select File/Import/and chose import the (generic text *.txt *.csv) extension; suddenly, a window appears named Import wizard. The user must check or select the delimited tab bottom, and then press next. In the next window, user must check or select the latitude field correspond to the column with latitude data, and the same for longitude. Frequently, the latitude is the (Y) labeled column and the longitude is the (X) column of data. Then, user must press the finish bottom and create the template style, at this step, it is very important to choose the label selected column, could be names, or maybe the number of the case, in the order they became sick. The user can choose the label to display over each point and can choose the color and the figure for the marks. Having as a result the .kst extension file to save. It appears at the left panel as a GE™ world symbol that contains the marks, to see the marks individually, must double click the GE™ world symbol that contains a folder with all marks. And finally, there is the layer of geocoded addresses, that represent the cases imported from Excel with all attributes (Video 1 available at: https://youtu.be/29BR7NM52XY).

It is very important to know that layers like a .shape extension files can be imported from GEPro™, so the atlas with borders, layers of cities, rivers, and more can be imported and become part of the map with the distribution of cases, represented by placemarks.

3.8 Sending the file by mail and format compatible to GIS programs

Any mark, polygon, route, layer, or group of them can be saved as a file and exported in formats compatible to classic GIS apps and programs; just save the place or mark or group of marks. The format is KML or KMZ file, which can be sent by mail to a person with GE™ or classic GIS preferred program installed on PC, or tablet, or phone. The person will be able to see the saved information display instantaneously.

The public health systems and databases should incorporate that geocoded data for the surveillance of infectious diseases transmission, not only for arboviruses vector-transmitted diseases but also for respiratory and several infections that become of interest, mainly those under international surveillance. For example, the next figure is a print screen of GE™ view, that shows marks with a label, that is the number of the case, and left clicking the mark, displays attributes or information from dengue patient number 40 reported by the medical service from a rural town of Costa Rica, that occurred on 2022 (Figure 2).

Figure 2.

Print screen of left click over a placemark labeled 40, which represents the 40th case of dengue with attributes shown, numbers arranged by symptom onset. Figure created by the author of the chapter.

4. Conclusions

Any epidemiologist can map the cases of vector-transmitted diseases with an Excel attributes sheet and geocoded addresses, importing the data from Google Earth Pro™, for a better space, time, and person analysis that is free and easy.

Acknowledgments

To the Ministry of health of Costa Rica, where the science, the sanitary legislation, and health regulations have permitted to preserve care of the public health, by the emission of health politics that establish the guidelines for the attention of patients identified by public and private health providers, and for the actions that allow the control of epidemics, and for the opportunities offered by this governmental institution for professional growth, for a great epidemical surveillance system.

Conflict of interest

“The author declares no conflict of interest.”

Notes/thanks/other declarations

Thanks to the public education of Costa Rica. Thanks to my family.

Video materials

Video 1. Mapping an excel sheet with geocoded data on Google Earth Pro, for epidemic surveillance. Created by the author for a better interactive user’s guide. Available from: https://youtu.be/29BR7NM52XY.

Acronyms and abbreviations

GE™

Google Earth™

GEPro™

Google Earth Pro™

KML

Keyhole markup language

KMZ

Keyhole markup zip

GIS

Geographic Information System

.csv

Comma separated values

.tab

Tabulation separated values

.kst

Google Earth style template

PC

Personal computer

GPS

Global position system

Arbovirus

Arthropod borne virus