What do we mean by IACC?

We’ve been using a term that may be unfamiliar to some: IACC, which stands for Infection-Associated Chronic Conditions. This blog explores what the term means, why it’s useful, and how it relates to other acronyms and evolving terminology.

What are IACCs?

IACCs refer to a group of chronic medical conditions that appear to be triggered by an infection. There are many illnesses in this category: ME/CFS, Long COVID, POTS (postural orthostatic tachycardia syndrome), fibromyalgia, and others, but they’ve historically been studied in isolation. These “siloed” approaches often limit research funding and slow scientific progress.

The growing use of umbrella terms like IACC reflects a grassroots effort to encourage science and medicine to examine these conditions side-by-side, looking for shared mechanisms rather than focusing only on their differences. This shift offers hope for better understanding and, eventually, more effective treatments.

The Pandemic as a Turning Point

At BHC, we often say that one “silver lining” of the COVID-19 pandemic has been a broader recognition that serious chronic illness can follow an acute viral infection. Public awareness of Long COVID has grown quickly, and with it, a deeper understanding of ME/CFS and related conditions.

We’ve worked hard to seize this moment to expand awareness of ME/CFS, which has long been considered a post-viral condition.

But It’s Not Always Straightforward

It’s important to note that not everyone with ME/CFS remembers having a clear infection just before becoming ill. Some people trace the onset of their condition to a hospitalization, physical trauma, environmental exposure, vaccination, or other trigger. These lived experiences are valid and recorded in research, but they rarely offer conclusive proof about the underlying cause.

Why? Because such events may involve multiple stressors to the body’s systems, including reactivation of latent viruses, immune system shifts, or other physiological disruptions. It’s often impossible to say definitively whether a virus, or which one, led to the illness.

Infections That Can Lead to Chronic Illness

That said, we do know that several viruses are associated with persistent or relapsing illness, including:

Epstein-Barr virus (EBV) – Known for causing mononucleosis, or “mono” / “the kissing disease”

Cytomegalovirus (CMV) – A common virus that usually causes mild symptoms or none at all in healthy people; can be serious in immunocompromised individuals

HHV-6 (Human Herpesvirus 6) – A virus that often causes roseola, a common childhood rash and fever

Parvovirus B19 – Causes “fifth disease,” a mild rash illness common in children, known for the “slapped cheek” rash

Enteroviruses – A group of viruses that includes coxsackievirus (hand, foot, and mouth disease), echoviruses, and non-polio viral meningitis

West Nile virus – A mosquito-borne virus that can cause fever, and in rare cases, neurological disease

Influenza – Commonly known as the flu

Polio (Poliovirus) – Once widespread, causes polio, which can lead to paralysis

Ebola – Known for causing severe hemorrhagic fever and often associated with outbreaks in parts of Africa

Other chronic conditions may stem from non-viral infections. For example, giardiasis (caused by a protozoan parasite) and Lyme disease (caused by the bacterium Borrelia burgdorferi) can both result in long-term symptoms, even after treatment.

It’s also striking that most people who experience these infections don’t go on to develop chronic illness. Some have lingering symptoms for weeks or months before recovering. Others, just a small fraction, develop ME/CFS or a related condition such as POTS, fibromyalgia, or irritable bowel syndrome (IBS).

Genetics may also play a role. For example, people with hypermobile connective tissue disorders may be more vulnerable to post-infectious or multi-system conditions. All of these factors make it difficult to identify clear pathways to illness, and even harder to develop targeted treatments.

Terminology: A Work in Progress

Adding to the complexity, there’s no universal agreement on how to label this group of conditions.

• Some use IACC (Infection-Associated Chronic Conditions)
• Others prefer IACD (Diseases) or IACI (Illnesses)
• Some avoid the word “infection” altogether and use CCC (Complex Chronic Conditions)

When BHC and the Open Medicine Foundation launched the MERC (Medical Education Resource Center) collaboration, we anticipated these differing perspectives. To be inclusive, we adopted the broad term msCCD (multisystem Chronic Complex Diseases) for our education platform.

Moving Forward, Together

BHC does not endorse a single term over another. What matters most is that the scientific and medical communities commit to studying these complex conditions seriously and to caring for those affected by them. Every terminology framework brings something useful to the conversation.

Progress will come not from arguing over labels, but from uniting around shared goals: greater understanding, better treatments, and compassionate care.

Let’s keep moving forward.