Objectives:Salmonella is a major public health concern particularly in areas of low socioeconomic status (SES) and high temperature. In this chapter, we examined several socioeconomic and environmental factors that may increase the spread of Salmonella in the southern states of the USA.
- Salmonella infection
- socioeconomic status
- climate change
- global warming
Contaminated eggs and poultry meat are common source of human salmonellosis. Wide range of domestic and wild animals, such as poultry and swine, can act as reservoirs for
Emergence or resurgence of numerous infectious diseases is strongly influenced by environmental factors, such as climate or land use change . Climate, weather, topology, hydrology and other geographical characteristics of the crop-growing site may influence the magnitude and frequency of transfer of pathogenic microorganisms from environmental sources .
2. Geographical variation and socioeconomic status effects
Socioeconomic status (SES) is an important predictor of diseases. SES is frequently measured based on individual and community-level education, income, wealth, employment and family background when compared with other individuals or groups. Low SES is generally associated with greater morbidity and mortality of diseases . Socioeconomic and demographic indicators can be used to predict the individuals and communities that are at an increased risk of acquiring infections. Generally, low socioeconomic status is an important predictor of several poor health outcomes including chronic diseases, mental illnesses and mortality.
In our previous study , we examined the extent of
Results of the study showed mostly positive correlation between low socioeconomic variables and increased rates of
Results of this study also revealed
2.1. Poverty, education and unemployment
Underreporting of enteric infections is a critical issue in disease surveillance systems. Generally, patients with severe symptoms tend to visit the doctor and are subsequently notified to health authorities. As of 2011, almost 23% of Mississippi populations are living under poverty with average per-capita income of $32,000, although rural per-capita income lagged at $29,550, according to the USDA Economic Research Service. There are 96 hospitals in Mississippi, 163 Rural Health Clinics, and 21 Federally Qualified Health Canters that provide services at 170 sites in the state. An average of 19% of Mississippi residents lacks health insurance [12, 13].
The west-central region of Mississippi showed higher rates of
Geographical variations in poverty rates were also observed in different districts of the state (Figure 2). In the Delta region of Mississippi, the poverty rate was 44.2%. The lowest
The northern region of the state including northeast, northwest, Tombigbee and Delta district had the highest rates of unemployment. An average of 42% increase in unemployment rate was observed in the region in 2011. Primary care provider rate was the lowest in the northwest and east-central regions of Mississippi. An average of 17% decrease in primary care provider rates was observed in these regions. On the other hand, highest rates of primary care providers were found in west-central and southeast regions of the state, with 2% increase from 2010 to 2011.
Our results are different from reported individual level epidemiologic studies that had found higher levels of foodborne infections among low education and low-income groups. Studies suggested that high socioeconomic status (HSES) groups may be overrepresented in incidence statistics. It is possible that lower socioeconomic status (LSES) groups tend not to have health insurance or do not seek medical care when needed due to financial constraints. Access to health care may be an important influence on rates of reported bacterial infections. In an economy without universal health care coverage, tendency to seek care for GI infection has been associated with having health insurance [17, 18]. However, the Affordable Care Act (ACA) is expected to expand insurance coverage to millions of people in the USA. As a result, rates of reported cases of diseases and infections are expected to increase. In future projects, we will try to understand the impact of Affordable Care Act of 2010 on diseases reporting, especially among minority and LSES groups.
It is quite possible that various SES groups have different exposures because of dietary differences, or differences in food safety behaviours . Behavioural studies have revealed that high SES groups are more likely to eat undercooked foods, such as raw oysters and rare beef [9, 12]; while low SES groups are less likely to have adequately cool refrigerators .
Other studies had similarly utilised GIS to examine the relationships between area-based socioeconomic measures and incidence of salmonellosis [18, 19]. The results showed higher incidences of salmonellosis in groups with high education compared to the less educated groups suggesting the role of education in health-seeking behaviour and the predisposition for
Neural network modelling was shown to be a useful tool in this study to predict the correlation between socioeconomic factors and
In the USA, Mississippi ranked 50th among all the states for health care, according to the Commonwealth Fund, a non-profit foundation working to advance performance of the health care system. For the past 3 years, obese populations were accounted for more than 30% of Mississippi's residents and 22.8 % of the state’s children. On top of obesity, Mississippi had the highest rates in the nation for high blood pressure, diabetes and adult inactivity .
Social and economic conditions underpin poverty and can directly or indirectly affect health status and health outcomes. Major epidemics emerge and chronic conditions cluster persist wherever poverty is widespread .
3. Effects of climatic variables
Diseases associated with climate change are estimated to comprise 4.6% of all environmental risks and hazards. Climate change, in the year 2000, contributed to about 2.4% of all diarrhoea outbreaks in the world, 6% of malaria outbreaks in certain developing countries and 7% of the episodes of dengue fever in some industrial countries. In total, the estimates showed that climate change related mortalities were 0.3%, whereas the related burden of disease was 0.4% .
Global average temperature, from 1906 to 2005, has warmed by 0.74°C; and since 1961, sea level has risen on average by 2 mm per year. On the other hand, Arctic sea ice has declined by 7.4% per decade while snow cover and glaciers have diminished in both hemispheres . The climate change rate is faster now than in any other period during the last 1000 years. According to the United Nations Intergovernmental Panel on Climate Change, average global temperatures will increase between 1.8 and 4.0°C in next 90 years along with sea level rise of 18–59 cm [30, 31].
Changes in expected weather patterns can lead to the transfer of microbial contaminants to leafy vegetables and herbs. Dry periods can cause dust storms that settle dust particles on leafy vegetables. The rate of microbial growth was shown to increase with rise in temperature. It influences the population of insects and pests found in and around farms that transfer human pathogens to leafy vegetables as well. Relative humidity has been shown to have an effect on survival of human pathogens . Climate change scenarios predict a change distribution of infectious diseases with warming temperature and changes in outbreaks associated with weather extremes, such as flooding and droughts.
Several infectious agents, vector organisms, non-human reservoir species, and rate of pathogen replication are sensitive to climatic conditions. Both
The southern states, including Mississippi’s climate, has been fluctuating with extreme patterns. The average temperatures in Mississippi have varied significantly over the past century, with an average of 1°F increase, since the late 1960s. Extreme rainfall events, primarily thunderstorms, have increased as well. While rainfall totals have changed little, seasonal trends are apparent, summers have become slightly drier and winters slightly wetter . On an average, 29 tornadoes are reported annually in Mississippi; the highest number was in 2008 with 109 tornadoes. In addition, during the past decade, Mississippi had experienced multiple hits by hurricanes including the devastating Katrina in 2005 .
Global warming and the climate change have contributed to the spread of several foodborne pathogens [5, 30]. In our previous research, we determined the extent of
Analysis of variance was performed to determine the seasonal change in
Our results indicated an increase in temperature is positively correlated with
The positive relationship between temperature and
The US-southern states climate is generally warm and wet, with mild and humid winters. The average annual temperatures in the region have increased by about 2°F since 1970, and the average annual temperatures in the region are projected to increase by 4 to 9°F by 2080 . Climate change and extreme events may increase the spread of foodborne diseases in this region, particularly in the disadvantaged states, such as Mississippi.
Studies showed that an increase in the ambient temperature correlated positively with an increase in human
There is consistent evidence that gastrointestinal infection with bacterial pathogens is positively correlated with ambient temperature, as warmer temperatures enable rapid replications of pathogens.
Higher ambient temperatures are main concerns on farm and during food processing and should be considered as an early warning for increased numbers of foodborne infections with 4–6-week lag time. Heightened surveillance during such times may act as a mitigation and enhance the preventive measures. Proper hygiene during slaughter, processing, wholesale and retail sale should be carefully implemented and monitored for further safeguards. More importantly, active consumer education through mass media and other sources regarding the potential danger of consuming contaminated food with
3.2. Precipitation effect
In our previous study , no correlation between monthly average precipitation rate and
A study by Jiang
Climatic changes impact the emergence or re-emergence of infectious disease agents. There are some general principles of pathogen emergence, which are associated with changes in ecology and agriculture, technology and industry, globalization, human behaviour and demographics, epidemiological surveillance and microbial adaptation [52, 53]. It is important to recognise that pathogen emergence usually occurs as a consequence of a combination of two or more specific factors .
4. Modelling approaches
4.1. Regression analysis
Multiple regression analysis were carried out to test the relationship between
4.2. Neural network modelling of
Neural network models for temperature effects on
Over the last few years, artificial neural networks, as nonlinear modelling techniques, had been proposed for use in predictive microbiology [55–61]. In our study, two neural network models, General Regression Neural Network (GRNN) model and Polynomial Net model, were used to predict the effects of temperature on
Monthly data for temperature and
Advanced NNs were selected and the simulated data files were imported. The network was built by defining input variables as poverty, uninsured, unemployment and primary care providers’ rates, while
4.3. GIS mapping
A GIS incorporates hardware, software and data for capturing, managing, analysing and displaying all forms of geographically referenced information.
Study area for GIS map: Mississippi (32.9906° N, 89.5261° W) is located in the southern USA. It is bordered by TN on the north, Gulf of Mexico on the south, AL on the east and Arkansas and LA on the west. It covers a total area of 47,689 square miles. GIS allows for the integration and analysis of geographic data, such as coordinates and area perimeters, and tabular data (i.e., attributes of geographic data points). Data are imported into mapping software in layers, where each layer represents a different visual component of the map. Shape files are layers which provide visual output of coordinates and area perimeters on the map.
Mississippi counties’ data were grouped by public health districts. Background map was obtained from ESRI ArcGIS online resources. Maps’ layers for
Human foodborne illnesses are significant public health concerns. Socioeconomic status and climate changes contribute to the increased rates of
Modelling approaches, such as neural network were shown to be a useful tool to model and predict outbreaks. Neural network models accounting for non-linearity may predict better association than regression models. Geographical information system mapping was also shown to be a very useful instrument to map and visualise the areas and districts of highest
Regression and neural network models were used to determine the correlation between increase in temperature and increase in
The reported research work is funded by the National Institute on Minority Health and Health Disparities of the National Institutes of Health under Award Number G12MD007581. The content is solely the responsibility of the authors and does not represent in any form or shape the official views of the National Institutes of Health.