The Epidemiology of Rickettsial Diseases on the US Mexico Border: An Analysis of Incidence Rates, Clinical Presentation and Risk Factors Associated With Rickettsia rickettsii, Rickettsia typhi and Ehrlichia chaffeensis Infection Público

Buelow, Michelle Lynn (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/3t945r026?locale=es
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Abstract


Abstract

The Epidemiology of Rickettsial Diseases on the US Mexico Border: An Analysis of
Incidence Rates, Clinical Presentation and Risk Factors Associated With Rickettsia
rickettsii, Rickettsia typhi and Ehrlichia chaffeensis Infection

By Michelle L. Buelow


Rickettsia rickettsii, Rickettsia typhi and Ehrlichia chaffeensis are three pathogens that
can cause severe morbidity and mortality when not properly diagnosed and effectively
treated. Because of their nonspecific clinical presentations, there are many challenges in
their diagnosis, causing rickettsial diseases to be under-recognized and underreported.
The goal of this study is to describe the burden and analyze epidemiological risk factors
of rickettsial diseases in patients presenting with syndromic febrile illness between 2007
and 2008 in two South Texas counties. As a part of the Binational Infectious Disease
Surveillance (BIDS) program, 1,392 patients with undifferentiated febrile illness were
enrolled at surveillance sites in Cameron County and Webb County, Texas. Serological
testing was conducted for the presence of antibodies and corresponding titer levels of R.
rickettsii, R. typhi and E. chaffeensis and cases were classified according to standard
CSTE protocols.1, 2 We found that rickettsial diseases occurred with increased incidence
at the U.S. Mexico border compared with statewide and nationwide estimates. Risk of
infection with all three pathogens increased with exposure to the outdoors. However,
none of the pathogens were significantly associated with multiple border crossings, the
use of protective equipment (such as insect repellent or protective clothing) or a reported
history of an insect bite. The study population in Cameron County was significantly more
likely to be infected with R. rickettsii and R. typhi than those in Webb County. The risk
for infection with both R. rickettsii and E. chaffeensis was significantly associated with
time progression through the study period. Risk of infection with R. typhi was
significantly associated with increasing age, while male gender was significantly
protective for infection with R. typhi. This study demonstrates the importance of
rickettsial diseases as emerging infections along the U.S. Mexico border and provides an
increased understanding of their risk factors. It also validates the importance of continued
binational collaboration in the BIDS project as a way to diagnose and implement public
health interventions with the hope of improving the health of the unique and dynamic
communities living in the U.S. Mexico border region.


Table of Contents

TABLE OF CONTENTS


DISTRIBUTION AGREEMENT ............................................................................................................... I
ABSTRACT ......................................................................................................................................... IV
ACKNOWLEDGEMENTS ........................................................................................................................ VI
LIST OF TABLES AND FIGURES ........................................................................................................... IX
BACKGROUND/LITERATURE REVIEW ............................................................................................... 1
MORBIDITY, MORTALITY AND INCIDENCE OF RICKETTSIAL DISEASES ....................................................... 1
CLASSIFICATION OF RICKETTSIAL DISEASES ........................................................................................ 3
THE TRANSMISSION, CLINICAL PRESENTATION, DIAGNOSIS AND TREATMENT OF R. RICKETTSII .................. 4
THE TRANSMISSION, CLINICAL PRESENTATIONS, DIAGNOSIS AND TREATMENT OF E. CHAFFEENSIS ............ 7
THE TRANSMISSION, CLINICAL PRESENTATIONS, DIAGNOSIS AND TREATMENT OF R. TYPHI ........................ 9
EPIDEMIOLOGICAL RISK FACTORS OF RICKETTSIAL DISEASES ................................................................. 10
CHALLENGES OF PASSIVE SURVEILLANCE OF RICKETTSIAL DISEASES ..................................................... 14
RICKETTSIAL DISEASES IN MEXICO ................................................................................................... 15
THE US/MEXICO BORDER REGION ......................................................................................................17
BINATIONAL INFECTIOUS DISEASE SURVEILLANCE PROGRAM .................................................................. 20
GOALS AND SIGNIFICANCE ............................................................................................................. 25
STATEMENT OF NEED ........................................................................................................................ 25
GOAL ..............................................................................................................................................25
AIMS .............................................................................................................................................. 25
SIGNIFICANCE ................................................................................................................................... 26
STUDY SETTING ................................................................................................................................. 28
SAMPLING METHOD AND ENROLLMENT CRITERIA .................................................................................... 29
SAMPLE COLLECTION ........................................................................................................................... 30
DATA ANALYSIS ................................................................................................................................. 31
Classification of Cases ......................................................................................................................... 31
Binational Case Definition ................................................................................................................... 32
STATISTICAL ANALYSIS .........................................................................................................................32
RESULTS ...........................................................................................................................................35
DEMOGRAPHICS ....................................................................................................................................35
CLINICAL PRESENTATION .......................................................................................................................... 36
INCIDENCE RATES ...................................................................................................................................... 38
EPIDEMIOLOGICAL RISK FACTORS- UNADJUSTED ..................................................................................... 39
Rickettsia rickettsii ............................................................................................................................... 39
Rickettsia typhi ..................................................................................................................................... 40
Ehrlichia chaffeensis ............................................................................................................................ 41
EPIDEMIOLOGICAL RISK FACTORS- ADJUSTED .......................................................................................... 42
Rickettsia rickettsii ............................................................................................................................... 42
Rickettsia typhi ..................................................................................................................................... 43
Ehrlichia chaffeensis ............................................................................................................................ 44
DISCUSSION ......................................................................................................................................... 50
EPIDEMIOLOGICAL FINDINGS ..................................................................................................................... 50
INCIDENCE RATES ....................................................................................................................................53
STRENGTHS AND LIMITATIONS .................................................................................................................. 55
CONCLUSIONS/ PUBLIC HEALTH IMPLICATIONS ........................................................................ 57
REFERENCES .........................................................................................................................................59
SIGNATURE FORM FOR NON-RESEARCH PROJECTS .................................................................. 62


LIST OF TABLES AND FIGURES
 Table 1: Final Case Classification of Each Pathogen ........................................................ 34
Table 2: Demographic Characteristics of Study Population ............................................. 45
Table 3: Prevalence of Signs and Symptoms of Probable Cases by Pathogen ................. 46
Table 4: Incidence Rates of Rickettsial Diseases in Webb and Cameron Counties in 2007
Compared to Reported National and Statewide Texas Incidence Rates ................... 47
Table 5: Unadjusted Bivariate Analysis of Probable Cases by Pathogen ......................... 48
Table 6: Adjusted/Multivariate Analysis of Probable Cases by Pathogen ........................ 49

Figure 1: Life Cycle of Rickettsia rickettsii ...................................................................... 21
Figure 2: Life Cycle of Ehrlichia chaffeensis .................................................................... 22
Figure 3: Life Cycle of Rickettsia typhi ............................................................................ 22
Figure 4: United States-Mexico Border Region ................................................................ 23
Figure 5: Cameron County, Texas ..................................................................................... 23
Figure 6: Webb County, Texas .......................................................................................... 24

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