Infectious diseases are infections or diseases that are caused by micro-organisms like bacteria, parasites, protozoa, fungi, or viruses. A person can be exposed to these organisms in the environment or they can be transmitted by another person or organism. These infectious diseases can be considered as an epidemic, spreading throughout a population, or an endemic, when the occurrence of disease is at a constant rate.  The specialist in this field is called Infectious Disease Specialist (ID Specialist), Doctor of Infectious Diseases, or Infectious Disease Physician. These medical doctors are responsible for investigating cases of infection and seeking the cause and cure for that specific type. They are also involved with the prevention, diagnosis, control, and treatment of infections. Aside from the common infectious diseases like the common cold or flu virus, ID specialists focus on diseases that are rarer in nature.


Educational Requirements


Bachelor’s Degree

Just like any other specialist in the medical field, an Infectious Disease Specialist must first complete a pre-medical bachelor's degree program. This undergraduate program should cover courses that will serve as the initial foundation of knowledge in science, laboratory work and instrumentation, and understanding on the basic concepts in medicine. There is a wide range of courses that a student who plans to be an ID specialist can take. Science programs, like BS Biology for example, are popular choices because these programs most likely include the courses that provide the basic information necessary for taking the Medical College Admissions Test or MCAT. These programs are also most likely to contain courses that will provide theoretical and practical knowledge essential to continue pursuing medical school.

In some states, it has also a recommended practice for college students to consult a medical school adviser in order to have a clearer understanding on the steps they need to take and courses and knowledge required pursuing the profession that they want. This will help the students plan their courses over their three to four years of undergraduate education. It is also highly recommended for aspiring medical students to partake in activities that will expose them in the field of medicine and patient care. Local hospitals and organizations often provide these opportunities by allowing students to volunteer in community health centers, public and private hospitals, medical missions, and feeding programs.

Most respectable medical schools only accept students that are within the specific Grade Point Average (GPA) that their school set. That is why, to ensure a student's entry to their prospect school, the student should be aware of the GPA cutoff of that school and make sure that their own GPA is within the range. For students who haven't decided on the school that they want to apply to, it is recommended for them to maintain a 3.0 or higher cumulative GPA and also a 3.0 or higher GPA for all their science and laboratory work courses. A good working relationship with teachers and mentors can also go a long way. These authority figures can serve as guide and provide objective remarks on the student's work ethic, ability, potential, and overall professionalism. These people can also serve as references for the required letter of recommendation that will be submitted to the institution that they are applying to.



Medical College Admissions Test (MCAT)

The Medical College Admissions Test or MCAT is a test is usually taken during the junior or the senior year of the undergraduate degree. This test usually differs from one country to another. It is used to evaluate the student's knowledge and understanding on the fundamental concepts and theories of the applicable sciences that will be needed for medical school and professional practice. It also assesses the student's problem solving and critical thinking skills. Different schools have different MCAT score cutoffs so it is necessary for the student to be aware of it. In some countries, MCAT scores are acceptable up to three years, allowing students to take additional classes and gain more training and experiences between graduating from their bachelor's degree and starting medical school. The MCAT result of the student will be included to their other application requirements and will be submitted to the school or schools that they are applying to.


Medical School

After graduating from their bachelor's degree and passing the MCAT, students can apply or seek acceptance into their preferred medical school. Respected medical schools are very competitive in nature. A strong academic standing with a high GPA (especially in applicable sciences), a high MCAT score to further prove their knowledge in scientific principles and critical thinking skills, as well as good letters of recommendations can go a long way in ensuring a slot in medical school. Some medical schools may also require the student to undergo a formal interview as part of the application process. Extra-curricular activities such as volunteering at a hospital or medical missions can also help strengthen an application.


Medical school usually takes four years to complete. During the first two years, the students are usually exposed to in-class coursework. This period allows the student to further expand their knowledge in anatomy and physiology, biology, pathology, chemistry, and other necessary courses that will strengthen their foundation as a medical practitioner. An exam usually concludes these first two years. This exam is used to gauge the student's scientific knowledge and readiness to proceed to the next part where they will begin their practical work under direct supervision.


The last two years of the medical school program is dedicated to provide students patient care experience under direct supervision, part of the program is usually referred to as Rotations. This period allows the students to apply the concepts and skills that they have acquired on the first two years. During this period, the students will be able to experience wide variety of specialties and work environments that could help them bring out particular interests or skills. These new knowledge can help them further choose which specialty is right for them and help them identify their residency and fellowship choices. In the case of an ID specialist, this can help the student identify their focus-patient care, research, or investigation. The specialties for rotations usually include ambulatory medicine and emergency medicine, gynecology and obstetrics, internal medicine, pediatrics, psychiatry, and surgery. A test will usually be taken by the students at the end of the fourth year to evaluate their knowledge and skills as well as to determine whether or not they are qualified to proceed to a residency program.



The residency program is a hands-on experience. A future ID specialist must be able to finish three to four years of residency, usually as a doctor of internal medicine or pediatrics. The residency program provides a more hands-on experience in patient care and a real setting where the resident is trained to do extensive laboratory work under the supervision of an experienced doctor and teacher. This period also allows the student to be part of a research project and take on leadership roles. Testing methods and laboratory result interpretation techniques are also studied extensively.


Residency is often considered as one of the most stressful period of the students' education. That is why it is necessary that the students are able to maintain their focus and priority on their studies and responsibility as residents. Connecting with potential mentors and finding more about their own skills and interests will help the residents identify which sub-specialty would be well fit for them. Right after the residency program, these students will then be required to take a board certification exam for internal medicine. After becoming board-certified in internal medicine, the internist (a doctor in internal medicine) can then proceed to complete two to three years of fellowship training program in infectious disease.



The fellowship program is where the students will be able to focus on the education and training on the sub-specialty. For an aspiring ID specialist, this is a two to three year program where the student can focus on the study of infectious diseases entirely. It is necessary that the student has accomplished the pre-requisite education because it will serve as the foundation for understanding the essentials of infectious diseases and specializing in the field.


There are generally three major tracks available for fellowship training in adult infectious diseases namely:

  • Basic Investigator Track
  • Clinician Track
  • Clinical Investigator Track


All of these tracks generally consist of a 12-month core curriculum and another 12-26 months of fellowship training depending on the chosen track. For the clinician track, they are required to have another 12 months’ worth of fellowship training while for the Clinical Investigator and Basic Investigator, 24-26 months’ duration of fellowship training is required.


According to the FRIEDA Online Database by the American Medical Association (AMA), there are 146 fellowship programs available in the United States of America. Infectious disease specialists are also given the option to further specialize on one specific type of infectious diseases of on a specific disease in general (e.g. HIV/AIDS)


Board Certification and Licensing


The next step after the fellowship program is the board certification. This test is more specialized compared to the three exams taken during the medical school proper also known as United States Medical Licensing Examination (USMLE). It will also conclude the fellowship training in the subspecialty of the physician’s choice.


In order to qualify for the American Board of Internal Medicine (ABIM) board certification in Infectious Diseases, the prospective ID fellow should have completed 2-year fellowship training. The additional training requirement for both the Clinical Investigator and Basic Investigator tracks is not required for the board certification. The additional training requirement for the Investigator tracks is intended for acquisition of adequate research experience which will enable the fellow to become a competent investigator.


Licensure requirements differ from each state. ID specialists must be aware of the requirements for the states that they are planning to practice in. This might involve additional testing as well as submission of experience, test scores, and other documents.


Roles and Responsibilities

Infectious Disease Specialists combine their clinical skills with the laboratory skills in order to make an accurate diagnosis and provide an effective treatment plan for a wide range of infections in both acutely and chronically infected patients. They would often serve as consultants to other physicians when:

  • The infection is difficult to diagnose.
  • The infection is accompanied by high fever.
  • The patient is non-responsive to treatment.
  • A previous patient or a healthy person is planning to travel overseas or to a location where the infection risk is higher.
  • A patient with immunodeficiency conditions like those who need HIV/AIDS management.


In all the cases that an ID specialist handles, a specialized training and diagnostic tool as well as a thorough investigation to identify the cause of the infection is necessary to determine the best approach to treatment. To ensure the effectiveness of the treatment, ID specialists may perform the following procedures:

  • Thoroughly review the medical history of the patient in order to identify the possible causes of infection and the location where the patient got infected. The ID specialist might need to get a hold of the information regarding the patient's travels, interaction with an infected person or group, and activities that might have compromised the patient (e.g. sex or needle sharing).
  • Perform physical diagnostic examinations to identify the exact part or parts of the body affected by the disease. This may also help in identifying the weaknesses that the patient may have.
  • Order laboratory tests such as blood cultures, urine samples, and x-rays to further identify the specifics of the disease and its manifestations.
  • Determine how fast the disease spreads and how contagious it is. This will help the ID specialist develop a treatment plan and prevent other individuals from being infected.
  • Consult other medical specialists (e.g. surgeons, virologists, etc.) to complete the treatment of the patient.
  • Prescribe treatment that may include medications and/or surgeries to treat or eradicate the disease.
  • Work with researchers in order to be updated about developing diseases and the proper treatments for the diseases that pose a risk to their patient population.
  • Conduct seminars or talks to train and educate the patient population and their families on how the disease will affect their lives, how to prevent the spread of the disease, and the symptoms that needs to be monitored over time.
  • Prescribe vaccination regimen for the patient’s family to prevent the spread of disease.


During the course of the treatment, ID specialists review the medical data that is obtained through clinical and laboratory tests. They may also need to perform medical procedures that are needed to treat or further diagnose the disease. These include:

  • Central venous catheter insertion- the insertion of a thin flexible hollow tube into a large vein for the introduction of fluids and/or medication.
  • Lumbar puncture- the withdrawal of cerebrospinal fluid through a hollow needle that is inserted into the lower part of the spinal canal. This is used to diagnose the disease or inject medication.
  • Sigmoidoscopy- examination of the intestine (or a part of it) with the use of a very small camera.



According to the U.S. Bureau of Labor Statistics, there is a predicted increase of 14% in the employment opportunities for all physicians and surgeons from 2014 to 2024. This is a faster rate than the average rise and the mean salary among physicians and surgeons in 2015 was $222,760. In the Medscape Infectious Disease Physician Compensation Report, it is stated that the average income of an ID specialist ranges from $125,000 to $250,000 with an average income of $170,000. The Northwest regions of the United States provide the highest average compensation for ID specialist with an average of $300,000. This region includes Alaska, Washington, Oregon, Wyoming, Idaho, and Montana. The South Central United States (which includes Texas, Oklahoma, and Arkansas) on the other hand has the lowest average compensation at $137,000.


Generally, the highest paid work setting is the private work setting where the physician is the owner of the practice and the lowest paid work setting is an outpatient clinic. The average income is greatly affected by work setting and situation. Here is a brief break down of pay by work setting and situation:


Work Setting

  • Academic: $151,000
  • Healthcare Organization: $134,000
  • Hospital: $170,000
  • Multispecialty group practice: $223,000
  • Single specialty group practice: $188,00
  • Solo practice: $225,000
  • Outpatient Clinic: $132,000

            Work Situation

  • Employee: $162,000
  • Independent Contractor: $175,000
  • Owner, solo practice: $259,000
  • Partner: $186,000




Even before the discovery of the microscope and the microorganisms that cause infection, evidence of infectious diseases as well as their effects on populations has been recorded. Scientists have found evidence of smallpox in 3000-year-old Egyptian mummies and some Egyptian papyrus paintings even depict infectious diseases such as poliomyelitis. These diseases were often seen as results of events tied to culture or supernatural beliefs. Diseases were often viewed as a result of karma or punishment from divine entities. Some cultures even saw diseases as curses, acts of magic, body fluid imbalance, excess blood, or proof that demons exist.


The earliest recorded scientific observation of infectious diseases was that of Thucydides. He was a historian from Athens. In 430 B.C., he analyzed the behavior of the Plague of Athens and wrote about his general observations. He observed that places with higher populations produced more infected victims at a faster rate. He also noted that physicians that came in direct contact with the infected people have the highest chance of being infected themselves. He debunked the prevailing theory that the diseases were caused by “evil airs” or Miasma by recording incidents wherein the plague was transported from one place to another. He also wrote the very first record of acquired immunity by noting that the people that have recovered from the plague have developed immunity and is not affected by future attacks from that specific plague.


Hippocrates wrote about the spread of diseases by means of airs, water, and places. He also made an association between climate, diet, and living conditions. In the 1500s, Girolamo Fracastoro discussed the germ theory and proposed three routes of contagion namely: direct contact, fomites, and contagion from a distance (airborne). This has made the ideas of contagion more popular in Europe during the Renaissance period.


In the 1600s, a draper shop owner named Antonie van Leeuwenhoek advanced the science of microscopy by being the first to observe microorganisms. His development of the microscope allowed the scientists to visualize microorganisms. The knowledge about the cultivation and identification of microorganisms was made more popular and well known in the 1800s and it was used in the mid-19th century by two scientists named John Snow and William Bud in their work to demonstrate the contagiousness of typhoid and cholera through contaminated water. These two scientists implemented measures to prevent water contamination and were credited with decreasing epidemics in their towns.


The link between infections and the presence of certain microorganisms were further strengthened by Louis Pasteur’s discoveries of the principle of vaccination, microbial fermentation, and pasteurization. He also reduced mortality from puerperal fever and created the first vaccines for rabies and anthrax. His discoveries fortified the foundations of disease control and prevention.


The formulation of the Koch’s postulates in 1884 by Robert Koch and Friedrich Loeffler has established a causative relationship between a microbe and a disease. These postulates were used as a general guideline to identify pathogen but it was also recognized that some infectious agents were responsible for disease even though they did not fulfill all of the postulates. Edward Jenner along with Jonas Salk and Albert Sabin developed effective vaccines for smallpox and polio. This vaccine would later result in the eradication of smallpox and near-eradication of polio. The 19th century also gave rise to the world’s first antibiotic, Penicillin, which is discovered by Alexander Fleming. The increasing understanding on the nature of diseases and its manifestations resulted to broad control measures such as personal hygiene, community sanitation, and public health awareness. The importance of education and proper nutrition was also noted for its effect on infectious diseases.



Infectious Diseases: A general Guide


Infectious diseases rank as the second leading cause of death globally. Over half of the affected of these diseases are children under the age of five. In the United States alone, 170,000 people die each year due to infectious diseases making it the third leading cause of death.


Infectious diseases can either be passed from person to person, animal bites, ingestion of contaminated food or water, or being exposed to organisms in the environment. Along with the wide range of organisms causing, the infection comes a wide range of signs and symptoms, but it often includes fever and fatigue. Mild infections can be handled by the body’s immune system and would only require rest and home remedies, while some more life threatening infections may require medical attention and treatment.


General Signs and Symptoms


General signs and symptoms common to majority of infectious diseases are:

  • Coughing
  • Diarrhea
  • Fatigue
  • Fever
  • Muscle and joint aches


If these signs and symptoms started to appear, it is advisable to have yourself checked up. Immediate medical attention is also highly recommended if the person is having difficulty in breathing, has severe headache with fever, experiences rash or swelling, have sudden vision problems, has been coughing for more than a week, has unexplained or prolonged fever, or has been bitten by an animal.


The easiest way to be infected is by coming in contact with an infected person or animal. Below is a more detailed explanation on the three ways that infectious diseases can spread:


Modes of Infection


Direct Contact

  • Person to person- this is the most common way for an infectious disease to spread. The direct transfer of bacteria, viruses, or other microorganisms from one person to another can occur when an infected individual touches, kisses, or coughs or sneezes on a non-infected person. It can also spread through the exchange of body fluids through sexual contact. In some cases, the person who passes on the infectious disease exhibits on sign or symptom and is only a carrier of the disease.
  • Animal to person- infected animal bites or scratches can transfer infectious diseases and can be fatal at times. Even handling animal excretions can transfer infectious diseases (e.g. toxoplasmosis infection can be acquired by scooping an infected cat’s fecal excretions).
  • Mother to unborn child- some microorganisms can pass through the placenta and infect the unborn child. Some microbes in the vagina can also be transferred to the baby during birth.


Indirect Contact

  • Through infected objects- some organisms can stay on inanimate objects (e.g. doorknobs, tabletops, or toilet seats) for a longer time and can be picked up by a person upon touching the object. If the person then touches his/her mouth, nose, or eyes before washing his/her hands, that person may become infected.
  • Insect bites- some microbes are spread by insects such as mosquitoes, fleas, lice, or ticks.
  • Food contamination- contaminated food allows the disease to spread to many people by a single source, which is why it is important to observe proper food preparations and packaging.




Personal hygiene is an important factor in order to prevent the spread of infectious diseases. Aside from keeping oneself clean by washing your hands and bathing regularly, a person can decrease the risk of getting infected or infecting others by:

  • Getting vaccinated
  • Staying home when ill
  • Preparing food safely by keeping the kitchen and kitchen materials clean as well as refrigerating leftovers.
  • Practicing safe sex by using condoms
  • Not sharing your personal items
  • Researching about the common diseases in the places that you want to travel to.
  • Consulting your doctor regarding the preventive measures you can take (e.g. vaccines) before traveling to a high risk area.




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