Yoav Golan, MD, MS, FIDSA, attending physician and associate professor of medicine at Tufts University School of Medicine, Boston, MA, explains risk factors for infection as well as key principles of infection prevention in patients with acute myeloid leukemia (AML).
To best understand how to prevent infection in patients with AML, one has to first understand what puts them at risk for infections. There are several components to that. One is exposures, such as food, water, pets, etc. Another has to do with the fact that these patients get treatment and the disease itself makes them immunocompromised, so their immune systems are not as potent in protecting them from infections. Other factors that contribute to the risk of infection have to do with very extensive exposure to the healthcare system and having a lot of procedures and lines that violate the integrity of their mucosal surfaces.
The principles of preventing infections in AML patients, in fact, to a large extent, determine the outcome of those patients as they go through therapies that can weaken their immune systems. Therefore, they are very important to understand. One of the principles is to avoid unnecessarily risky exposures, and that includes food-related issues. Raw foods, for example, have to be avoided. Well water should be avoided, as well as should some exposures to animals. For example, one should not clean the litter of his cat. Another important component is preventing exposure to sick people, and we are surrounded by a lot of sick people during the winter period, but also throughout the year. Those exposures should be prevented. In addition to that, vaccination is really important, including vaccination of those people with whom they interact in their everyday life. So, if you have a relative that has AML, it’s really important for you to get a flu shot so you don’t get the flu and don’t infect someone who cannot really cope with the flu.
Other components of infection prevention include infection control and better precautions. So good hand hygiene; cleaning your hands is very important for patients, and using a mask every once in a while when going into the public, particularly during the height of treatment, is extremely important. The last component that protects our patients, and on which we are going to focus a little more today, is going to be antimicrobial prophylaxis.
To understand the risk of infection in AML patients it is important to understand what’s causing this risk and particularly what’s causing neutropenia, which is the main risk factor for infection in this patient population. It is important to understand what makes these patients immunocompromised so that we can monitor that and we can prevent them from getting infected while at the height of the immunocompromised state.
Neutropenia is typically defined as a neutrophil or ANC count of less than 1500, with real neutropenia typically defined as less than 1000, and severe neutropenia is defined as less than 500. Now, many of the guidelines to determine who is at the highest risk of infection use a cutoff of 100, and anyone who is expected to be lower than 100 is expected to be at high risk of an infection.
The neutropenia in patients with AML is really of multifactorial causes. One of the causes of neutropenia is, in fact, the disease itself. The expansion of one clone of white cells will prevent other white cells from flourishing and the diversity of those neutrophils—not necessarily their number—would be reduced. The expansion of this clone in the bone marrow will prevent the production of new neutrophils and will result in neutropenia as well. Because AML is a disease of the immune system, the treatments of AML target the immune system and add to this immunocompromised status. Most chemotherapy medications that are used in leukemia further deplete the number of neutrophils and are the main reason for neutropenia during therapy in patients with AML.
Another reason for neutropenia could be some viruses that can infect those patients, such as cytomegalovirus, that have an effect on the bone marrow that is suppressing. Another reason could be some specific infections that can fill the bone marrow and prevent neutrophils from being produced.