Study explores prevalence and symptom trajectory of long COVID

A recent study posted to the Research Square* preprint server estimated long-term coronavirus disease 2019 (COVID-19), or, long COVID, and the trajectory of disease symptoms in a representative sample in the US.

Study: Long COVID and Symptom Trajectory in a Representative Sample of Americans. Image Credit: Dmitry Demidovich/Shutterstock
Study: Long COVID and Symptom Trajectory in a Representative Sample of Americans. Image Credit: Dmitry Demidovich/Shutterstock

Various studies have reported that many patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) suffer from a variety of health problems long after symptom onset. However, there is a lack of clarity regarding the prevalence, manifesting symptoms, and risk factors associated with long COVID.

About the study

The present study used survey data of US adults to estimate the prevalence of long COVID adjusted according to baseline symptoms, report the commonly observed long COVID symptoms, and identify long COVID risk factors.

Data were obtained from the Understanding America Study (UAS) COVID-19 national sample which is a national ongoing probability-based internet panel of almost 9000 non-institutional US adults. Participants were randomly selected from households from a list of postal service addresses across the US. They answered the survey online on any device of their choice. From 1 April 2020, follow-up surveys were performed every two weeks, during which participants were asked to fill out the survey.

Participants were considered COVID-positive following a positive SARS-CoV-2 test or a positive diagnosis by a healthcare professional. Furthermore, a participant was diagnosed with long COVID if they were presenting symptoms at the time of diagnosis, which were absent four weeks prior to COVID-19 diagnosis and were present 12 weeks after.

Self-reported symptoms were monitored four weeks prior to COVID-19 diagnosis, at the time of diagnosis, and 12 weeks after. The study monitored the occurrence of fever, runny nose, chest congestion, cough, sore throat, sneezing, body or muscle aches, headaches, fatigue or tiredness, shortness of breath, abdominal discomfort, vomiting, hair loss, dry skin, body temperature above 100.4 F or 38.0 C, diarrhea, lost sense of smell, and skin rash.

The participants answered the symptom-related questions with “Yes”, “No”, and “Unsure” responses. The team then generated a symptom count variable ranging between zero and 18 by adding up the number of reported symptoms per wave for each participant.

The team considered variables like age, sex, race, education level, and smoking status of all the participants. They also examined pre-existing health conditions associated with a higher risk of long COVID-19 such as diabetes, cancer, heart disease, high blood pressure, asthma, chronic lung diseases such as chronic obstructive pulmonary disease (COPD) or emphysema, kidney disease, autoimmune disorders such as rheumatoid arthritis, and obesity.


The survey was conducted between 10 March 2020 and 31 March 2021. It consisted of 8,425 participants, including 872 COVID-19-positive individuals, of which the team analyzed 308 COVID-19 diagnosed participants. The study cohort had a median age of 46 years with 57% females and 22% Hispanic, 61% non-Hispanic White, and 12% non-Hispanic Black participants. Also, 18% of the participants had diabetes, 9% had heart disease, 5% had cancer, 29% had high blood pressure, 5% had chronic lung disease, 19% had asthma, 4% had kidney disease, 24% were obese, and 5% had an autoimmune disorder.

A total of 40% of the COVID-19-infected patients reported at least one symptom 12 weeks post-diagnosis. However, after taking into account the presence of pre-infection symptoms, 23% experienced a minimum of one COVID-19 symptom 12 weeks post-diagnosis. At the time of infection, 45% of the participants had body aches, 43% had fatigue, 41% had a cough, 40% had a headache, 37% had a fever, 35% had a runny or stuffy nose, 33% experienced loss of smell, 29% had diarrhea, 28% had a sore throat, 25% had shortness of breath, and 25% had chest congestion. A total of 80% of participants reported symptoms and had an average symptom count of six.

The proportion of reported symptoms peaked during the infection with a subsequent reduction with the proportions remaining higher than that of the pre-infection stage. Also, in comparison to the pre-infection stage, the proportion of participants reporting abdominal discomfort, sore throat, loss of smell, and a body temperature above 100.4°F was higher at the post-infection level.

Moreover, symptoms reported by most of the participants at the post-infection level were fatigue, dry skin, runny or stuffy nose, headache, and sneezing. In the pre-infection stage, the most reported symptoms were headache, runny or stuffy nose, abdominal discomfort, fatigue, and diarrhea.

Notably, long COVID patients had a higher number of symptoms as opposed to other patients. Also, long COVID patients were more likely to be obese and reportedly experienced more headaches, hair loss, and sore throat at the time of infection. Interestingly, people who had chest congestion had a lower risk of long COVID.

Overall, these findings could serve as a foundation for future research to extensively analyze the prevalence, risk factors, and persistent symptoms of long COVID.

*Important notice

Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Bhavana Kunkalikar

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.


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