Confirmed and reported cases of COVID-19 have a wide range of symptoms from mild complaints, such as fever and cough, to more critical cases associated with difficulty in breathing . Some of the most common symptoms include cough, fever, chills, shortness of breath (SOB), muscle aches, sore throat, unexplained loss of taste or smell, diarrhea, and headache . Symptoms can start as mild and become more intense over 5 to 7 days, worsening if pneumonia develops in patients . Approximately, 1 out of 6 infected individuals become seriously ill and develop difficulty in breathing, especially in the elderly with underlying health conditions .
A meta-analysis study of COVID-19 patients, as depicted in Fig. 1, showed fever (88.8%) as the most common symptom, followed by dry cough (68%) and fatigue (33%) . Other symptoms noted were productive cough (28.5%), SOB (17%), muscle pain (14.4%), sore throat (11.4%), and headache (10.2%) . The least common symptoms were diarrhea (4.4%), nausea and vomiting (4.1%), rhinorrhea (3.2%), abdominal pain (0.16%), and chest pain (0.11%) .
Symptoms of COVID-19 may appear anytime from 2 to 14 days after exposure; therefore, 14-day quarantine is recommended . The average incubation period for COVID-19 is approximately 5.2 days . In Wuhan, China, the most common symptoms observed from the onset of this outbreak include fever, cough, and fatigue, while some features that were not so prevalent were sputum production, headache, hemoptysis, and gastrointestinal (GI) symptom such as diarrhea [12, 13]. Another study that was conducted in Beijing, China, showed that the average age of patients with COVID-19 was 35.5 years and had a mean of 3.5 days from the onset of symptoms to admission in the hospital . The same study also showed that fever was present in 87.5% of patients, which persisted for 6.5 days, and symptoms resolved 2.5 days after a negative test result .
Some individuals who are infected do not develop any symptoms at all, and about 80% of positive cases recover from the disease without any treatment . However, there have also been instances of transmissions of COVID-19 from one person to another before the person became aware of being sick, or the symptoms were so mild that the person did not know he/she had the illness . It becomes essential to seek medical attention immediately if a person suspects that he/she may have been infected or is a confirmed case of COVID-19 experiencing respiratory distress, has blue lips, is in constant pain, or has pressure in the chest . Also, it is important to note that COVID-19 is more infectious than SARS-CoV and MERS-CoV due to its numerous epidemiological and biological characteristics .
Due to COVID-19 being a relatively new and understudied disease, the data available is limited. However, from the cases that emerged, it was observed that comorbidities increase the chances of infection . Based on current information and clinical expertise, the elderly, especially those in long-term care facilities, and people of any age with serious underlying medical conditions are at a greater risk of getting COVID-19 . The elderly, a vulnerable population, with chronic health conditions such as diabetes and cardiovascular or lung disease are not only at a higher risk of developing severe illness but are also at an increased risk of death if they become ill . People with underlying uncontrolled medical conditions such as diabetes; hypertension; lung, liver, and kidney disease; cancer patients on chemotherapy; smokers; transplant recipients; and patients taking steroids chronically are at increased risk of COVID-19 infection .
A meta-analysis study on COVID-19 comorbidities, as depicted in Fig. 2, had a total of 1786 patients, of which 1044 were male and 742 were female with a mean age of 41 years old . The most common comorbidities identified in these patients were hypertension (15.8%), cardiovascular and cerebrovascular conditions (11.7%), and diabetes (9.4%) [10, 17]. The less common comorbidities were coexisting infection with HIV and hepatitis B (1.5%), malignancy (1.5%), respiratory illnesses (1.4%), renal disorders (0.8%), and immunodeficiencies (0.01%) .
Patients with moderate to severe asthma are at a disadvantage because this virus affects their respiratory tracts, leading to increased asthmatic attacks, pneumonia, and acute respiratory distress . According to the CDC’s morbidity and mortality weekly report, 34.6% of patients aged 18 to 49 years old have an underlying chronic lung disease, such as asthma . In Iran, a case study reported that genetic predisposition to COVID-19 can increase the probabilities of getting infected with SARS-CoV-2 and can lead to death from this virus . This genetic predisposition was seen in 3 brothers in Iran who were 6 years apart in age (54, 60, and 66) years who died due to COVID-19, despite no identified comorbidities and living separately from one another . As of January 2, 2020, Wuhan, China, had 41 patients admitted to the hospital who tested positive for COVID-19, of which 73% (30/41) were men with a median age of 49 years old, 66% (27/41) of these patients had been exposed to the Huanan market, 32% (13/41) had underlying diseases such as diabetes 20% (8/41), hypertension 15% (6/41), and cardiovascular 15% (6/41) . Patients who are HIV positive, along with a low CD4 count and not on antiretroviral therapy, have a higher risk and incidence of other medical issues including COVID-19 . According to the International Aids Society (IAS), people who are human immunodeficiency virus (HIV) positive, taking antiretroviral treatment, and do not have a low CD4 count will have the same risk of having COVID-19 as one without HIV [19, 20].
As depicted in Fig. 3, a population-based surveillance report via COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) reported clinical data on 1478 COVID-19-positive patient hospitalizations from March 1 to March 30, 2020 . Among the 1478 patients studied, 12% of adults showed clinical data of underlying medical conditions with the most prevalent being hypertension (49.7%) and obesity a close second (48.3%) . Other medical conditions included chronic lung disease (34.6%), diabetes mellitus (28.3%), and cardiovascular diseases (27.8%) .
COVID-19 can cause severe disease leading to hospitalization in ICU and potentially death, especially in the elderly with comorbidities . According to the CDC, 8 out of 10 deaths reported in the USA occurred in adults 65 years old and above . Roughly 80% of COVID-19-positive cases result in full recovery from the illness without any hospitalizations or interventions . There are still many facts that we do not know about COVID-19 due to gaps in knowledge; therefore, many studies are underway to better understand this virus .
Wuhan, China, had 41 patients admitted to the hospital who tested positive for COVID-19 from December 16, 2019, to January 2, 2020, and the clinical outcomes are shown in Fig. 4 . Of the 41 patients with confirmed COVID-19 in the hospital, 100% had pneumonia, 29% developed acute respiratory distress syndrome (ARDS), 15% exhibited an acute cardiac injury, and 12% acquired a secondary infection . The majority of these patients (68%) were discharged, 17% remained hospitalized, 10% ended up in the ICU, and 15% ended in death .
From February 20 to March 5, 2020, a study was conducted in Evergreen, Washington, on the characteristics and outcomes of 21 critically ill patients with confirmed COVID-19 diagnosis . This study showed that 71% of these patients required mechanical ventilation and acute respiratory arrest was seen in all of them . Within 72 h of developing ARDS, 53% of these patients showed increasing severity of respiratory problems, leading to poor short-term outcomes and a higher risk of death . As of March 17, 2020, the mortality rate was 67% in these patients, with 24% critically ill and 9.5% discharged from hospital .
As shown in the CDC’s mortality and morbidity weekly report in Fig. 5, case mortality increased as the patient’s age increased [21, 23]. Among the age group ≤ 19 years, no ICU admission or mortality was reported . COVID-19 has also been noticed in children, but the disease took a more moderate course when compared with adults. The prognosis was also seemingly better, and deaths were infrequent .
On April 29, 2020, WHO reported over 3 million confirmed COVID-19 cases worldwide, with over 200,000 of these cases resulting in mortality . The majority of these deaths are within the USA with over 50,000, followed by Italy with over 25,000 and Spain with over 20,000 . New York is being hit the hardest by the novel coronavirus spreading across the USA, with more cases and deaths per capita than any other state. Table 1 reports that over 86% of COVID-19 deaths involved at least one comorbidity, according to the New York State Department of Health .