Title
Pertussis epidemic in California, 2010:

Potential links to socio-economic factors and ethnicity.

Author

Krysta Rogers
American River College, Geography 350: Data Acquisition in GIS; Fall 2010
Contact Information: (rogersk5@imail.losrios.edu)

Abstract

Pertussis, or whooping cough, is a human disease that causes fits of coughing in older children and adults; in infants and young children pertussis can cause severe complications and even death. California has been experiencing a pertussis outbreak since January 2010. Over 6,700 people have been affected; there have been 10 infant deaths due to pertussis. Many factors can influence disease occurrence. I compared the number of pertussis cases per county with factors such as median household income, number of uninsured individuals, and ethnicity. There was no clear connection between pertussis cases and any of the factors. However, there appeared to be a slight correlation between median household income and number of pertussis cases. Counties with high median household income had higher incidence of pertussis cases.

Introduction

Pertussis, or whooping cough, is a disease caused by the bacterium Bordetella pertussis. Although clinical symptoms can vary, pertussis is usually characterized by severe attacks of coughing that lasts for at least 14 days (CDC 2010). Although a vaccine for the prevention of pertussis has been in use since the 1940s (Wood & McIntyre 2008), pertussis remains one of the most poorly controlled human diseases in many countries throughout the world with localized outbreaks occurring periodically. Outbreaks of pertussis are believed to be due to no or incomplete childhood vaccinations or through waning immunity received from prior vaccination in older children and adults (Curry 2007; Top et al. 2010). Many factors may influence the occurrence of a particular disease. It is important to assess all data before making assumptions about how disease outbreaks occur.

My objectives are to correlate disease occurrence, in this case pertussis, with socio-economic factors such as income, health insurance coverage, ethnicity, and total population of each county.

Background

The most recent outbreak of pertussis is occurring in California where over 6,700 cases of pertussis have been reported between 1 January and 16 November 2010 (CDPH 16Nov2010 Report). The last major outbreak in California occurred in 1947 with 9,394 cases and in 2005 with 3,182 cases (Figure 1). The current outbreak in California has resulted in the death of 10 infants, 9 of which were Hispanic. Infants less than 3 months of age have been most affected by pertussis; infants of this age have not yet received vaccination for pertussis and are highly susceptible to infection. Rates of infection are highest among Hispanics with an infection rate of 17.9 cases per 100,000 individuals and whites with 14.7 cases per 100,000 individuals reported. Hispanic infants less than 6 months of age have the highest age-related incidence rates (Figure 2).

These statistics, as presented by the California Department of Public Health (CDPH 16Nov2010 Report), have lead to some discussions about the factors that are driving this current pertussis outbreak. In particular, due to the high incidence reported in Hispanics, the role of ethnicity in disease spread has been discussed. Articles have been written that discuss the perceived link between ethnicity to the increased incidence of pertussis in California (Lin 2010). While some ethnicities may be more susceptible to certain diseases, there are many, often interrelated, factors that influence disease outbreaks and transmission. Some of these include access to health care and other preventative services, as well as income and social factors.

Figure 1. Yearly number of reported pertussis cases in California. Graph from the California

Department of Public Health Pertussis Report for November 16, 2010 (CDPH 16Nov2010).

Figure 2. Incidence of pertussis cases by age group and ethnicity or race in California. Graph from the California Department of Public Health Pertussis Report for November 16, 2010 (CDPH 16Nov2010).

Methods

1. Pertussis outbreak data

Information regarding the current pertussis outbreak in California was obtained from the California Department of Public Health website (CDPH 16Nov2010 Report). Periodic updates are reported and include case counts, age and ethnicity incidence rates, and pertussis rates by county. I utilized the report containing outbreak information gathered between 1 January and 16 November 2010 (CDPH 16Nov 2010 Report).

I input Pertussis case counts for each county in California into a Microsoft Excel spreadsheet. In this spreadsheet, I also included each county’s FIPS code to join to other data within ArcMap and longitude and latitude in decimal degrees in NAD 83 for the relative center of each county. The coordinates were used to display case count information for each county. I added the Excel table to an ArcMap document and plotted the coordinates for each county to display the pertussis case counts as points within each county. I then exported these points into a new layer and added the layer to ArcMap.

2. Health insurance coverage data

Health insurance coverage data was obtained from the United States Census Bureau (US Census 2007). The Bureau’s Small Area Health Insurance Estimates (SAHIE) Program reports information regarding number of individual’s uninsured for each county in California for the year 2007. Data were complied into a Microsoft Excel spreadsheet and again, FIPS codes were included to join this data to other data in the ArcMap document.

3. Median household income data

Median household income for each county in California was obtained from the Bureau of Labor Statistics, Local Unemployment Statistics data of the US Census Bureau’s Small Area Income and Poverty Estimates Program (US Census 2008). Median household income data were from 2008. Data were originally presented in text format delimited by spaces. Data were imported into an Excel spreadsheet to be utilized in ArcMap.

4. Ethnicity data

Ethnicity data were obtained from the US Census Bureau (US Census 2000). Ethnicity by each county was presented in an Excel spreadsheet. Data are from the 2000 census.

5. Base layer data

A base map of California, major cities, and county boundaries were obtained from the Cal-Atlas website (Cal-Atlas 2010). A county layer that contained georeferenced 2000 US Census data was obtained from a previous GIS class. The health coverage, household income, and ethnicity table data were joined to the counties layer by the FIPS code for map presentation.

Results

The results from this project are presented in graphic format. The maps depict the general relationship between pertussis cases and various socio-economic factors, ethnicity, and total population size for each county. More analyses need to be conducted to identify the interconnectedness of these factors.

Five maps are presented. The first map relates pertussis cases in California with the number of uninsured people in each county. The second map presents medium household income by county. The third and fourth maps, relate pertussis cases in each California county with ethnicity; map three shows Hispanic population per county and map four shows Caucasian population per county. The fifth map shows pertussis cases and total population size per California county.

Figures & Maps

Map 1: Pertussis Epidemic and Number of Uninsured by County.

Map 2: Pertussis Epidemic and Median Household Income by County

Map 3: Pertussis Epidemic and Hispanic Population by County

Map 4: Pertussis Epidemic and Caucasian Population by County

Map 5: Pertussis Epidemic and Total Population by County

Analysis

Map 1: Pertussis cases and number uninsured by county. Health insurance coverage might be an indication of disease risk. That is, you might expect more pertussis cases reported in counties with a higher number of uninsured residents. However, after reviewing the map, it does not seem to show a correlation between pertussis and number uninsured.

Map 2: Pertussis cases and median household income by county. As with health coverage, income might be related to disease risk. Households with low income could have limited access to preventative health care, such as vaccinations. However, the map shows almost the opposite of this assumption; some of the counties with the highest median household income levels have high numbers of pertussis cases. For example, many counties in and around the Bay Area from Sonoma and Napa counties south to Santa Cruz and Santa Clara, as well as Ventura and Orange counties, have some of the highest median household incomes in the state. These counties also have relatively high numbers of Pertussis cases.

Map 3: Pertussis cases and Hispanic population by county. Although the CDPH reports high incidence of pertussis cases in Hispanics, there is not a clear relationship between the incidence of pertussis and the Hispanic population.

Map 4: Pertussis cases and Caucasian population by county. Again, there was not a clear relationship between pertussis cases and the Caucasian population.

Map 5: Pertussis cases and total population by county. When the total population of each county is compared to pertussis cases, it resembles a similar pattern to the other ethnicity maps. This indicates that counties with higher populations are more likely to have higher incidence of pertussis cases.

Conclusions

California has the largest number of uninsured people in the United States. (CHCF 2009). In addition, California families with an annual income less than $25,000 are the most likely to be uninsured. Furthermore, Hispanics are more likely to uninsured than any other ethnic group in California with Hispanics making up almost 60% of California’s uninsured. However, when compared to the rest of the United States, individuals in California of all other ethnicities are equally as likely to be uninsured (EBRI 2000). While you might assume people with low income or are uninsured to have higher incidence of disease, this may not be true in the case of the current pertussis outbreak. Counties with high numbers of uninsured individuals and low household income levels did not appear to be related to the incidence of pertussis cases. However, there appeared to be a slight correlation between high household income and pertussis cases. There are a few factors that may explain this apparent relationship.

A few articles have suggested one of the reasons for the high frequency of pertussis cases in counties with high median household income has to do with the increased likelihood wealthy families to opt out of childhood vaccinations for their children for “personal beliefs” (Iannelli 2010; Jewett 2010; Simmins 2010). Due to the increased media attention given to childhood vaccines and a perceived higher risk of autism in children, many parents have declined to vaccinate their children. In addition, California law does not require children to get booster vaccinations before entering middle school. This is a particular concern because immunity from vaccines received as an infant has declined by the time children reach 10-12 years old making them more susceptible to diseases like pertussis. As a result of the current pertussis outbreak, a bill was passed in September to require all children entering 7^th to 12^th grade to show proof of pertussis vaccination (CDPH 30Sept2010).

Of course, it would be unwise to draw to many conclusions solely from mapped data. While the data used to produce the maps may be accurate, the interpretation of the data may vary. As such, it is important to verify data quality to ensure you are utilizing the best available data. This means researching the source of the data and any associated information available. When presenting the data, it is critical to provide as much background information as possible so the user can determine if the data is accurate. Another potential concern is comparing data gathered in different years. Utilizing data from different years, especially if some of the data is greater than 5 years old, the information may no longer be accurate. Obviously it is best to gather data that was collected in a similar time frame.

References

California Department of Public Health (CDPH). Pertussis Report November 16, 2010. (CDPH 16Nov2010 Report)

California Department of Public Health (CDPH). Early Alert to Health Care Providers: Assembly Bill 354 Becomes Law, 2011 Pertussis (Whooping Cough) Immunization Requirements for Students. September 30, 2010. (CDPH 30Sept2010)

California Health Care Foundation (CHCF). California Health Care Almanac. California’s Uninsured, December 2009. (CHCF 2009)

Centers for Disease Control and Prevention (CDC). Pertussis signs and symptoms. (CDC 2010)

Curry, K. 2007. Pertussis: a reemerging threat. Journal for Nurse Practitioners, February, pages 97-100.

Employee Benefit Research Institute (EBRI). Special Report SR 36. September 2000. Washington, D.C. 32 Pages. (EBRI 2000)

Iannelli, V. 2010. About.com Pediatrics Blog. Whooping cough outbreak continues in California. 5 November 2010. (article)

Jewett, C. 2010. California Watch Blog. How California state law helps whooping cough spread. 25 July 2010. (article)

Lin II, RG. Los Angeles Times Blogs. Q&A on whooping cough: are illegal immigrants fueling the outbreak? State officials say no. 16 September 2010. (article)

Simmins, C. Yahoo Associated Content. California’s whooping cough epidemic centered in rich, white counties. 12 November 2010. (article)

State of California. Cal-Atlas Geospatial Clearinghouse. (Cal-Atlas 2010)

Top, K.A., B.A. Halperin, D. Baxendale, D. MacKinnon-Cameron, and S.A. Halperin. 2010. Pertussis immunization in paediatric healthcare workers: Knowledge, attitudes, beliefs, and behaviour. Vaccine 2169-2173.

United States Census Bureau. Ethnicity data, 2000. (US Census 2000)

United States Census Bureau, Small Area Health Insurance Estimates. 2007 Health Insurance Coverage Status for Counties, California. (US Census 2007)

United States Census Bureau of the Census, Small Area Income & Poverty Estimates Program. Bureau of Labor Statistics, Local Area Unemployment Statistics data, 2008. (US Census 2008)

Wood, N. & P. McIntyre. 2008. Pertussis: review of epidemiology, diagnosis, management, and prevention. Paediatric Respiratory Reviews 9: 201-212.

links
non-tables page || index page || || original