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Cases in Clinical Infectious Disease Practice

Obtaining a good history from the patient remains the cornerstone of an accurate clinical diagnosis: Lessons learned in many years of clinical practice



Okechukwu Ekenna




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Table of Normal Laboratory Values*

Component Unit Reference range
White blood cell K/UL 4.4–10.1 (4400–10,100/μL)
Hemoglobin g/dL 10.0–18.0
Hematocrit % 37–50
Platelets K/UL 117–369
MCV fL 82–99
Neutrophils (polymorphonuclear leukocytes) % 43.7–84.9
Eosinophils % 0.6–6.0
Lymphocytes % 8.4–40.7
Erythrocyte sedimentation rate mm/hour 0–20
C-reactive protein mg/dL 0.00–0.30
O2 saturation % 95–99 (arterial/capillary); >74 (venous)
Glucose (fasting) mg/dL 65–99
Blood urea nitrogen mg/dL 7–18
Creatinine mg/dL 0.6–1.3
Sodium mmol/L 135–148
Potassium mmol/L 3.5–5.3
Alanine aminotransferase (serum glutamic pyruvic transaminase) IU/L 12–78
Aspartate aminotransferase (serum glutamic oxalo-acetic transaminase) IU/L 15–37
Albumin g/dL 3.4–5.0
Alkaline phosphatase IU/L 45–117
Total bilirubin mg/dL 0.2–1.0
Lactate dehydrogenase IU/L 84–246

* Adapted from the 2015 Singing River Health System Adult Normal Laboratory Values. Variations with age and sex are not reflected here. These values are to be used only as a general guide.

Okechukwu Ekenna, MD, MPH, D(ABMM), FACP

Dr Ekenna was born in Aba, Nigeria, where he had his primary school and most of his secondary school education (Dennis Memorial Grammar School in Onitsha). He spent a year as an exchange student at Loughborough Grammar School in Leicestershire, England, and another year in Germany, at Neusprachliches Gymnasium Aue, in Wuppertal-Elberfeld. General Certificate of Education (GCE, Advanced Level) was acquired following attendance at the Modern Tutorial College in London.

He attended medical school at Philipps-Universitaet Marburg/Lahn, Germany, graduating in April, 1979 (Aerztliche Pruefung). He successfully defended his doctoral thesis in June, 1979 (magna cum laude) and spent a year of medical internship in Germany before moving to the United States for Residency and Fellowship trainings in Internal Medicine, Infectious Diseases,and Post-Doctoral Fellowship in Medical Microbiology.

Through the course of his clinical and teaching experiences, he has served as consultant physician and lecturer to several institutions in Nigeria (University of Maiduguri Teaching Hospital) and in the USA. He is presently Adjunct Associate Professor of Medicine (since 1998)at the University of South Alabama, in Mobile, AL. He is in private practice in Pascagoula, MS,and is Consultant in Infectious Diseases to the Singing River Health System (SRHS). He is the Chairman of the Infection Prevention/Control Committee for SRHS. He has active consulting privileges at Ocean Springs Hospital and Singing River Hospital in Pascagoula, MS.

He is a naturalized citizen of the United States.

Dr Ekenna is a member of the American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, and Emerging Infections Network of the Infectious Diseases Society of America. He is a Fellow of the American College of Physicians and Fellow of the Royal Society of Tropical Medicine and Hygiene, London. He is also a member of the Organizing Committee of the African Initiative Group of the American Society for Microbiology.

Dr Ekenna is Board certified in Internal Medicine, Infectious Diseases, and in Medical and Public Health Microbiology. He is also certified in Clinical Tropical Medicine and Travelers' Health. He has a Master's degree in Public Health (MPH). He has authored multiple papers in peer-reviewed journals.

Dr Ekenna is fluent in Igbo (Nigerian), English, German, moderately so in French, and speaks a little Hausa. He is still trying to learn Spanish. His wife thinks of him as a history buff.


To my parents: Eze Raymond Onuoha Ekenna and Ugo-eze (Mrs) Gabraeline Urasi Ekenna (née Ezurike), and their recognition of the value of a good education.


First, I would like to thank the many patients presented here (who will remain anonymous), who have allowed me to tell their story and use their image to illustrate the clinical points made in this book. We are reminded every day that it is a privilege to care for patients who entrust their lives and well-being to our judgments, often working with incomplete or conflicting data. Many of the presented images have made it easier to tell the stories in this book.

I am grateful to the colleagues who asked me to see their patients and render an opinion. I thank them for their trust, and the confidence reposed in me. It is clear that sometimes there are no clear answers to the complex questions posed by these physicians and their patients.

I also thank the many journal and book publishers who gave us permission to use data and figures from their publications and resources. We have acknowledged them wherever indicated. Those illustrations have served to improve the presentation of the cases in this book.

The Singing River Health System gave permission and approval to use laboratory and demographic data, as well as radiologic images where applicable, without patient identifiers or infringing on patient confidentiality. I am grateful for their support.

Ms Cyndi Aycock, MLT (senior microbiologist), was particularly helpful in working with me to process and preserve many microbiological cultures and specimens over the years, many of which are depicted in this book. She did this with such enthusiasm. Thank you, Cyndi.

Dr Sid Eudy, pathologist, was gracious enough to prepare some of the micrographs used in this book.

Several of my friends and colleagues reviewed this manuscript and offered useful suggestions: John O. Chikwem, PhD, Professor of Microbiology and Immunology, Lincoln University, Lincoln, Pennsylvania; Keith Ramsey, MD, Professor of Medicine, East Carolina University, Greenville, NC, formerly Head of Infectious Diseases at the University of South Alabama (USA) in Mobile, AL, who first recruited me as adjunct faculty at USA; and Abraham Verghese, MD, Professor of Medicine and Vice Chair for the Theory and Practice of Medicine, Stanford University, CA.

Dr Christopher Paddock, of the Centers for Disease Control and Prevention, was kind enough to write a generous preface for me. I thank him immensely.

Ms Cynthia Davis, my office nurse, was very helpful in tracking down some of the patients, so that I could obtain their formal permissions to use their photographs in the book.

I am grateful to John Wiley & Sons, Inc., my publishers, and especially to Ms Mindy Okura-Marszycki and Ms Stephanie Dollan, for trusting me initially with this opportunity; to my project editor, Divya Narayanan, and Anandhavalli Namachivayam, production editor, for working with me intensely to get this book readied for publication on time.

The copy editor, Holly Regan-Jones did a wonderful job to help clear up ambiguities.

Finally, I would like to thank my wife, Chiazo, for her support and encouragement over the several years it took to put this book together. She encouraged me as I worked over the holidays to add small sections to the book, in between other clinical and family responsibilities.


In the spring of 2007, I received a call from a colleague at the Mississippi State Department of Health who informed me of a patient recently evaluated by an infectious diseases physician from the Gulf Coast. The patient had presented with fever, rash, and an eschar following the bite of a tick. At the time of the call, the patient was no longer symptomatic, for the physician had presumptively and correctly diagnosed the illness as rickettsial infection and prescribed the appropriate antibiotic; however, he was curious to know if there was a way to determine if this illness represented a recently recognized disease known as Rickettsia parkeri rickettsiosis. Remarkably, he had retained the tick removed by the patient. Working with the state health department, the tick was sent to our laboratory at the Centers for Disease Control and Prevention, where we determined that it was in fact infected by R. parkeri, closing the loop and establishing this little-known agent as the cause of the patient's illness.

This episode was my first interaction with Dr Ekenna, the astute infectious disease physician and author of this book. To place Dr Ekenna's diagnostic acumen in greater perspective, he diagnosed four more patients with R. parkeri rickettsiosis over the next several years, which is particularly remarkable when one considers that our laboratory at CDC has identified only about 40 patients with this disease in the entire United States since its discovery in 2002.

The case studies provided in this book are salient examples of Dr Ekenna's keen ability of medical detection, whereby the diagnosis and care of each patient are based on a careful history and physical examination. These fundamental processes represent the pillars of clinical diagnosis and are emphasized considerably during the training of medical students and residents; nonetheless, years of practice and experience are characteristically needed to hone and channel these skills to a level where they can be applied effectively and consistently. The cases described herein illuminate Dr Ekenna's deceptively simple and logical approach to each medical mystery in which he gathers pertinent data relating to person, place, and time and assembles a diagnosis and careful plan of treatment tailored to the complete circumstances of the individual patient. This truly is the art of medicine. In this context, we follow the diagnosis and successful treatment of a financially challenged patient with sporotrichosis, learn of the removal of carious teeth from a patient with Actinomyces israelii endocarditis, and observe the confirmation of a sulfa drug-induced hypersensitivity masquerading as sepsis in a long-suffering patient.

The breadth and scope of cases portrayed in this collection are fascinating. These include a wide spectrum of infectious conditions caused by various common and not so common infectious agents that include mycobacteria, fungi, helminths, spirochetes, and, of course, rickettsiae. Many of the infections are presented as syndromic or uniquely situational processes, such as a section on serious soft tissue infections caused by various Vibrio, Staphylococcus, and Alcaligenes species bacteria identified in patients along the Gulf Coast in the aftermath of Hurricane Katrina. Remarkably, these clinical vignettes originate not from the collective encounters by a large group of specialists at a tertiary care facility in a large metropolitan center, but rather from the professional experience of one doctor working at a small community hospital along the Mississippi Gulf Coast, and reflect the immeasurable good that a thorough and thoughtful physician can provide to the health and well-being of an entire region.

Christopher D. Paddock, MD, MPHTM
Centers for Disease Control and Prevention, Atlanta, Georgia


In the era of cost cutting and lack of adequate health insurance for many patients, clinical skills and time spent with patients are not adequately compensated. Yet these dwindling and underpaid skills – good history taking, observation of and listening to patients, and physical examination – remain essential to making and reaching a complete and accurate diagnosis. Expensive laboratory and imaging diagnostics, while very relevant, should not replace these age-old skills that have served to enhance and maintain the doctor–patient relationship and human connection, a connection that is often necessary for healing.

The process of differential diagnosis is particularly relevant in infectious diseases, and still involves what we typically label as “the art and science of medicine.” This process requires a skill that usually improves with clinical experience, and is not achieved by textbook reading alone.

I have had the privilege and requirement to present on a regular basis real cases seen in my private practice over the last 18 years to medical students, residents, fellows, and faculty as part of my teaching responsibilities with the University of South Alabama in Mobile, Alabama, as well as presenting to the local medical staff on the Gulf Coast of Mississippi. The positive feedback I have received from students, medical staff, and faculty has encouraged me to present some of these cases in this publication. The format chosen is similar to the way I have usually presented them at the teaching conferences, except that they will not be in PowerPoint and will be somewhat abbreviated because of space constraints.

These cases will provide an illustration of how the infectious disease clinician processes and integrates data to arrive at a diagnosis. This type of hands-on approach is not given adequate emphasis these days in our training programs.

The cases presented in this book will take the reader from the initial patient encounter, through the history and physical examination, to simple laboratory findings and stains, to a final diagnosis, in a way that is simple to follow and without the need to cram up a lot of other data.

The book is intended for the practicing clinician or student in clinical training. It should be useful to teaching hospitals involved in the training of medical residents and students of allied health institutions involved in clinical practice. An additional advantage is that the cases presented here do not reflect patients seen at tertiary institutions, but rather in the community setting. They reflect the type of cases or situations the resident or student is likely to encounter in the real world after training.

The cases presented in this book should be within the reach of the average practicing physician and medical resident in training. They should also help practitioners and students in allied health, who may work up clinical specimens referred by clinicians, in their understanding of the thinking of the consultant. The cases will include photographs, illustrations, and microbiological slides as applicable and available. I have added schematic diagrams on the few occasions where it was not possible to obtain permits for patient photographs.

It is hoped that reviewing these cases will enhance the integrated skills and critical thinking of the reader.

Finally, at the end of each case, I will discuss diagnostic aids or clues in the case and practical lessons learned.

How the book should be used and understood

The cases presented were seen between 1997 and 2015, an 18-year period, and include inpatients and outpatients.

The presentations reflect the time and period during which the patients (cases) were encountered. Diagnostic and treatment modalities, therefore, reflect those available at the time and place of care.

All of these cases were consultations provided to physicians practicing in the community setting (whether hospital based or in office practice).

All personal identifiers have been removed (including names of institutions where care was provided), in order to protect the identity of the patients.

However, the dates of patient encounters (consults) have been included for context, as well as the season of the year, as these may provide important epidemiologic clues to making a correct diagnosis.

My suggestion is that you first review the case history and then hazard a diagnosis before turning to the answer and discussion section.

At the end of each case presentation, we will address simple diagnostic clues and any lessons learned from the case.