What are the signs of post–acute infection syndromes?


The long-term health consequences of COVID-19 have refocused our attention on post–acute infection syndromes (PAIS), starting a discussion on the need for a complete understanding of multisystemic pathophysiology, clinical indicators, and the epidemiology of these syndromes, representing a significant blind spot in the field of medicine. A better understanding of these persistent symptom profiles, not only for post-acute sequelae of SARS-CoV-2 infection (PASC), better known as long COVID, but also for other diseases with unexplainable post-acute sequelae, would allow doctors to fine tune the diagnostic criteria. Having a clear definition and better understanding of post–acute infection symptoms is a necessary step toward developing an evidence-based, multidisciplinary management approach.


The observation of unexplained chronic sequelae after SARS-CoV-2 is known as PASC or long COVID.

Long COVID has been reported as a syndrome in survivors of serious and critical disease, but the effects also persist over time for subjects who experienced a mild infection that did not require admission to hospital. This means that PASC, especially when occurring after a mild or moderate COVID-19 infection, shares many of the same characteristics as chronic diseases triggered by other pathogenic organisms, many of which have not been sufficiently clarified.

PAIS are characterized by a set of core symptoms centering on the following:

  • Exertion intolerance
  • Disproportionate levels of fatigue
  • Neurocognitive and sensory impairment
  • Flu-like symptoms
  • Unrefreshing sleep
  • Myalgia/arthralgia

A plethora of nonspecific symptoms are often present to various degrees.

These similarities suggest a unifying pathophysiology that needs to be elucidated to properly understand and manage postinfectious chronic disability.

Overview of PAIS

A detailed revision on what is currently known about PAIS was published in Nature Medicine. It provided various useful pieces of information to assist with the poor recognition of these conditions in clinical practice, a result of which is that patients might experience delayed or a complete lack of clinical care.

The following consolidated postinfection sequelae are mentioned:

  • Q fever fatigue syndrome, which follows infection by the intracellular bacterium Coxiella burnetii
  • Post-dengue fatigue syndrome, which can follow infection by the mosquito-borne dengue virus
  • Fatiguing and rheumatic symptoms in a subset of individuals infected with chikungunya virus, a mosquito-borne virus that causes fever and joint pain in the acute phase
  • Post-polio syndrome, which can emerge as many as 15-40 years after an initial poliomyelitis attack (similarly, some other neurotropic microbes, such as West Nile virus, might lead to persistent effects)
  • Prolonged, debilitating, chronic symptoms have long been reported in a subset of patients after common and typically nonserious infections. For example, after mononucleosis, a condition generally caused by Epstein-Barr virus (EBV), and after an outbreak of Giardia lamblia, an intestinal parasite that usually causes acute intestinal illness. In fact, several studies identified the association of this outbreak of giardiasis with chronic fatigue, irritable bowel syndrome (IBS), and fibromyalgia persisting for many years.
  • Views expressed in the literature regarding the frequency and the validity of posttreatment Lyme disease syndrome are divided. Although substantial evidence points to persistence of arthralgia, fatigue, and subjective neurocognitive impairments in a minority of patients with Lyme disease after the recommended antibiotic treatment, some of the early studies have failed to characterize the initial Lyme disease episode with sufficient rigor.


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