Types of Infections

When we talk about infections, we refer to the germ and where the infection is found, for example a “strep throat” (Streptococcus in the throat).

Areas of the Body Where Germs Can Cause Infections

Sometimes your signs and symptoms can point to the place where the infection has occurred. For instance, feeling pain where fluids or drugs are given into a vein (intravenously or IV) that is red and swollen might tell you that the IV site is the source of infection. Or a shadow on a chest x-ray might suggest that you have a lung infection (pneumonia). The most common places in the body where infections are found are:

• Skin or soft tissue
• Mouth and throat
• Esophagus
• Sinuses
• Rectum, liver, or abdomen
• Vascular access device ( A small plastic tube that is threaded into a large vein in the chest, neck, or arm. It is used to draw blood and give IV medicines. You rarely have to be stuck with a needle when you have such a device.)
• Skin and tissue at an IV site
• Lungs
• Bladder and kidneys
• Central nervous system (brain and spinal cord)

Types of Germs That Cause Infections

Infections are grouped by the type of germ that causes them. The four main groups of germs are: bacteria, viruses, protozoa/parasites, and fungi. Most of the infections in patients with neutropenia are due to bacteria and viruses that normally live on the skin or in the gastrointestinal tract. Some are found in the environment. Generally, these germs do not cause infections when your defense systems are normal. But if your body’s defense system is weak from cancer treatments, the germs can begin to grow and damage your tissues. These infections are called opportunistic infections because the germs use your weak defense system as an opportunity to cause illness.

Like all living things, germs have scientific names that are made up of first and last names. These names tell us which germs may be alike in their actions. For instance, the names for house cats (Felis domesticus) and lions (Felis leo) tell us they are related. Likewise, Staphylococcus epidermidis and Staphylococcus aureus are related bacteria. But like house cats and lions, they differ in important details. Staphylococcus epidermidis rarely causes infections in healthy people, but it can cause infections in cancer patients who have an IV or plastic tube in a vein (to get fluids or chemotherapy) and a low white blood cell count. Staphylococcus aureus can cause very bad infections, and it often does not respond to many drugs that kill germs. Therefore, the infection can be hard to treat.

Although all germs and people have first and last names, those that are very well known are called by their first names. If you call only a first name, it may mean all varieties of that germ. For example, the name Staphylococcus includes all types of it, such as Staphylococcus aureus and Staphylococcus epidermidis. Like some people, germs with long names are sometimes known by their initials or nicknames. For instance, Escherichia coli is called E. coli, and Staphylococcus is commonly called “Staph.”

Bacterial infections

Bacteria are the smallest living germs, and they cause most infections in cancer patients.

Some names of bacteria that cause infections are:

• Pseudomonas aeruginosa
• Klebsiella pneumoniae
• Escherichia coli (E coli)
• Clostridium difficile
• Staphylococcus aureus ("Staph aureus")
• Staphylococcus epidermidis ("Staph epi")
• Pneumococcus
• Enterococcus
• Streptococcus

Viral infections

Viruses are the smallest known germs. Unlike bacteria, they are not "alive" because they cannot make new viruses on their own. Viruses can only make new viruses when they are inside living cells, such as the cells of humans.

Viruses that cause infections in cancer patients with low neutrophil counts are:

• The virus that causes cold sores and genital herpes (herpes simplex virus, or HSV)
• The chickenpox virus (varicella zoster virus, or HZV)
• Cytomegalovirus (CMV)
• Influenza and other seasonal viruses that cause influenza-like illness

Respiratory viruses such as influenza, respiratory syncytial virus (RSV), and other seasonal viruses

While a common cause of illness in normal individuals, these viruses may cause severe illness in people with weak immune systems. Pneumonia is the most serious respiratory virus infection, affecting the lungs. It is more likely to happen when a person with a weak immune system gets a respiratory illness. The best way to prevent influenza is to be vaccinated every fall with the “flu shot,” and have your immediate family members do the same. Frequent hand washing during times that these viral infections are common in your community will also help decrease the chance of these viruses spreading. You will want to avoid crowds and people with infections while your neutrophil count is low. (See “How to Reduce Your Risk of Infection”)

Fungal infections

In humans, fungi can live in balance with other germs that grow in the body without causing symptoms or tissue damage. But a fungal infection can occur when there is damage to the skin, a low neutrophil count, decreased immune function, or a long course of steroid medicines. Fungal infections in cancer patients are more likely if the patient has already had bacterial or viral infections due to neutropenia.

Fungi that most commonly cause infections in cancer patients are:

• Candida (yeast)
• Aspergillus and other molds
• Cryptococcus
• Histoplasma

Protozoal infections

Protozoa are considered the smallest and simplest form of animals. Although some protozoal infections can affect people with a healthy immune system, these infections are more common in less developed countries than in the United States. In the United States, most protozoal infections affect people with weak immune functions caused by organ transplants, cancer, AIDS, or other diseases. These germs are much less common than bacteria, viruses or fungi, but can occasionally lead to serious problems in the person with a weak immune system.

Common protozoa that can cause infections in people with cancer are:

• Pneumocystis jirovecii (previously known as P. carinii)
• Toxoplasma
• Cryptosporidium

Laboratory Tests to Diagnose Infections

If an infection is suspected, the following tests are usually done to diagnose the infection.

• Blood will be taken for a complete blood count and to check your neutrophil count.
• Blood will be taken for at least 2 blood cultures, usually from different sites. The blood cultures help find germs that are in the blood, which is normally free of germs. If you have one or more plastic tubes in a large vein for giving chemo­therapy or intravenous (IV) medicines, each tube site will be cultured.
• A urine sample may be taken for a urine culture.
• A chest x-ray will be taken to look  for pneumonia.
• Cultures are taken from body sites that might be the source of infection. For example, a throat culture may be done if you have a sore throat, or a stool  culture if you have diarrhea.

Cultures are done by taking body fluids or samples from a suspected site of infection, and placing them in a special broth or gel that helps the germs to grow. This solution or plate is incubated (placed in a warm location) for several days. Any germs that grow in the lab can then be identified under the microscope, or tested in other ways to learn exactly what type of germs they are. The culture process takes varying amounts of time, depending on how quickly the germ reproduces. Some germs grow slowly (like TB) and some grow quickly (like staph). Other special tests may be done if there are certain symptoms, or if the germ is hard to find.

Your doctor will want to know the exact type of germ causing the infection in order to give you the best treatment. Sometimes doctors can guess which germs are causing an infection in certain organs of your body, but tests are still needed to confirm it since different germs usually require different treatments. These tests (cultures) can take several days before the results are known. Because infections in cancer patients can progress quickly, you will receive treatment for the infection before testing is complete. Once the tests results confirm the germ causing the infection, your treatment can be changed if needed.

Sometimes, you can have an infection without any signs or symptoms. You might have samples of body fluid or body tissue tested if there is a very high risk of an infection (for instance, if your neutrophil count is very low). If an infection is found with the tests, treatment is started before symptoms begin.

In some cases, a fever can be present and the health care team cannot find the cause of the fever. This is called “fever of unknown origin,” meaning that a germ causing the infection cannot be found. If you have a fever while you have a low neutrophil count, you will be treated as though you do have an infection, even if the germ is not found. Your doctor will continue to look for a cause by looking for signs and symptoms, reviewing your blood tests, and, perhaps, repeating some tests.

Your doctor may refer you to an Infectious Disease specialist (a doctor who specializes in treating infections) for complicated situations. These specialists may recommend extra testing in an effort to figure out exactly what germs are causing your fever.

CAUSES OF FEVER AND NEUTROPENIA

TREATMENT OF FEVER AND NEUTROPENIA

For more information on these treatment guidelines, or on cancer in general, call the NCCN at 1-888-909-NCCN or the American Cancer Society at 1-800-ACS-2345. Or you can visit these organizations’ web sites at www.cancer.org (ACS) and www.nccn.org (NCCN).

© 2006 by the National Comprehensive Cancer Network (NCCN) and the American Cancer Society (ACS). All rights reserved. The information herein may not be reproduced in any form for commercial purposes or downloaded and stored in any information-retrieval system without the express written permission of the NCCN and the ACS. Single copies of each page may be printed out for personal, noncommercial use only.