**2. Post-COVID-19 conditions**

Although respiratory symptoms make up the majority of COVID-19's clinical presentation due to the SARS-CoV-2 infection, other conditions like pulmonary (such as pneumonia or dyspnea with exertion), gastrointestinal (such as anorexia or diarrhea), neurological (such as headache, anosmia, or dizziness), or even cardiac ones (such as ischemia, arrhythmias, or myocarditis) may also manifest. It is now well established that nearly a third of patients worldwide will have persistent symptoms for weeks and months, sometimes up to a year after being diagnosed with COVID-19 [7]. These results, particularly for patients who had severe symptoms and spent many weeks in intensive care, are comparable to the recovery from SARS in 2003. But COVID-19 is different because a large portion of those who do not need to be hospitalized seem to relapse, persist, or manifest new symptoms months after the initial infection [8].

When SARS-CoV and MERS-CoV outbreaks occurred in the past, people who recovered from these viral illnesses were left with lingering symptoms like extreme fatigue, a lower quality of life, protracted shortness of breath, and behavioral health issues. These symptoms have put a significant burden on the local health-care systems where the outbreak occurred. Similarly, despite scientific evidence that SARS-CoV-2 replication stops four weeks after the commencement of infection (on the basis of sampling viral isolates from the respiratory tract, not the nasopharyngeal/oropharyngeal sample), a collection of distinct clinical symptoms known as post-COVID-19 syndrome has been reported in a minority of patients who have recovered from COVID-19 caused by SARS-CoV-2 [9]. A meta-analysis including 4828 post-COVID-19 patients showed that symptoms and post-acute sequelae of SARS-CoV-2 can persist for weeks to months after the infection [10].

Persistent symptoms after the COVID-19 illness are called long-term COVID or post-acute sequelae of COVID-19. Some individuals who have contracted the virus that causes COVID-19 may go on to develop post-COVID conditions (PCC) or long COVID as a result of their infection. Long-haul COVID, post-acute COVID-19,

post-acute sequelae of SARS CoV-2 infection (PASC), long-term effects of COVID, and chronic COVID are only a few of the terms used to describe post-COVID problems [11].

The hallmark of post-acute COVID-19 syndrome is the continuation of clinical symptoms for longer than four weeks following the beginning of acute symptoms [9]. The term "post-COVID conditions" was created by the Center for Disease Control (CDC) to characterize health issues that last longer than four weeks after getting COVID-19. The following conditions fall under this category: multi-organ COVID-19 effects, impacts of COVID-19 treatment/hospitalization, and extended COVID or persistent post-COVID syndrome (PPCS) [9].

Clinically, "long covid" is characterized by symptoms such as weariness, dyspnea, exhaustion, brain fog, headache, persistent loss of smell or taste, cough, sadness, low fever, palpitations, dizziness, muscle and joint pain, and autonomic dysfunction [9, 12].

The multi-organ effects of COVID-19 include clinical manifestations involving the cardiovascular, pulmonary, renal, and neuropsychiatric organ systems, although the duration of these multi-organ effects is unclear [9, 13].

The long-term "effects of treatment or hospitalization for COVID-19" are similar to other severe infections. These include post-intensive care syndrome (PICS), which consists of impairment of cognition, psychological health, and physical function in an intensive care unit survivor. It can also include muscle weakness, problems with thinking and judgment, and symptoms of PTSD. Many patients with these complications caused by COVID-19 recover over time [9, 14].

In addition to morbidity and mortality in the acute phase, post-acute health problems and consequences have also been recorded in persons who have survived COVID-19. According to the review, up to 80% of patients with COVID-19 continue to complain of health problems after the acute infection and more than 50 side effects have been reported [15]. Post-acute COVID-19 was categorized as follows by Nalbandian et al. based on the severity of symptoms following COVID-19 infection: After the initial acute episode, subacute or persistent COVID-19 symptoms can last up to 12 weeks, and chronic or post-COVID syndrome symptoms start to show up after that. This should not, however, be attributed to a different diagnosis [16].

A large observational cohort study from 38 US hospitals assessed the outcomes of 1250 COVID-19 survivors 60 days after hospital discharge using medical record abstraction and telephone surveys. During the study period, 6.7% of patients died, while 15.1% of patients required readmission. Out of a total of 488 patients who completed the telephone survey, 32.6% of patients reported persistent symptoms including 18.9% with new or worsening symptoms. In this study, 159 individuals reported experiencing cardiopulmonary symptoms (e.g. cough or dyspnea), including 92 who experienced new or worsening symptoms and 65 who experienced irreversible loss of taste or smell. Fifty-eight patients reported new or deteriorating difficulties carrying out their everyday tasks. Among the 195 patients who had jobs prior to being admitted to the hospital, 117 were able to go back to work, while 78 were unable to do so due to continued health issues or job loss. Almost half of all patients (238 of 488) reported being emotionally affected by their health, and 28 sought mental health care after discharge [17].

Similar findings were obtained in studies conducted in Europe. In a populationbased prospective cohort study conducted in Spain to determine post-COVID-19 complications and risk factors among patients six months after SARS-CoV-2 infection, in a sample of 484 patients, it was shown that 160 patients (33.1%) experienced at least one post-COVID-19 problem after six months, and 47 of them (29.5%) sought medical help. Hair loss, exhaustion, loss of taste or smell, and headache were the most prevalent long-lasting effects. The complication's risk factors included female gender, age over 35 years, current smoker, and exposure to COVID-19. A third of patients had persistent symptoms compatible with long-term COVID-19 syndrome [18]. In 143 patients who were discharged from the hospital after recovering from acute COVID-19 at a median time of up to 60 days following the onset of symptoms, a post-acute outpatient clinic established in Italy revealed that 87.4% of patients had persistent symptoms. The most frequently reported symptoms were fatigue (53.1%), dyspnea (43.4%), joint pain (27.3%), and chest pain (21.7%), and 55% of patients continued to experience three or more symptoms. In this study, a decline in quality of life was noted in 44.1% of patients [19]. Also, a study conducted in Brazil confirmed the impact of COVID-19 on worsening health-related quality of life and mental health in COVID-19 patients three months after hospital discharge, compared to that before the onset of COVID-19 symptoms [20].

Other studies have reported similar findings. Results of a prospective follow-up study of 110 survivors in the United Kingdom, 8–12 weeks after hospital admission [21], and 277 survivors in Spain, 10–14 weeks after the disease onset [22], as well as survey studies of 100 UK COVID-19 survivors, 4–8 weeks after discharge [23], and 120 patients discharged from a hospital in France, 100 days after admission [24], showed that fatigue, dyspnea, and psychological distress, such as PTSD, anxiety, depression, and loss of concentration and sleep disorders, observed in approximately 30% or more of study participants at follow-up.
