The Centers for Disease Control and Prevention has expanded its list of possible symptoms of the coronavirus, a step that reflects the broad variation and unpredictability in the way the illness can affect individual patients.

Echoing the observations of doctors treating thousands of patients in the pandemic, the federal health agency changed its website to cite the following symptoms as possible indicators of Covid-19, the infection caused by the coronavirus:

chills

repeated shaking with chills

muscle pain

headache

sore throat

and, new loss of taste or smell.

Previously it had listed just three symptoms: fever, cough and shortness of breath.

The C.D.C. added the six symptoms earlier this month after new recommendations were issued by an organization of public health epidemiologists that is responsible for defining which infectious diseases are tracked and reported to the agency. The organization, the Council of State and Territorial Epidemiologists or C.S.T.E., recommended that Covid-19 be considered a nationally reportable illness and gave guidelines about how cases should be defined and identified.

The group’s recommendations say that cases should be reported if there are positive lab tests, but also if there are clinical symptoms that meet one of several thresholds. One category involves people who have cough, shortness of breath or difficulty breathing. Another involves people with two of the following symptoms: fever, chills, shivers, muscle pain, headache, sore throat or new dysfunction of taste and smell. Cases of people in both categories should be reported as likely Covid-19 only if there is no other more plausible diagnosis, the recommendations say.

While people who become seriously ill from coronavirus infection primarily have acute respiratory distress, other symptoms that accompany the disease can vary widely, doctors and researchers have reported.