This is a guest essay for Healthbeat. Public health, explained: Sign up to receive Healthbeat’s free national newsletter here.
Social media feeds filled up in recent days with reports of an outbreak in Russia of people with severe respiratory symptoms, including coughing up blood. According to these reports, tests for common viruses were negative, and there was fear this was caused by a new virus. As one journalist aptly observed, “The speed with which viral rumors can trigger public concern is a growing challenge for health officials in Russia and globally.”
Indeed, in the past year, I have become concerned about an epidemic of epidemic reports, a tendency for social and mainstream media to write about illnesses or deaths in other countries and speculate that a “mystery” infectious disease has emerged. Notable examples include “disease X” in Congo from October to December 2024, human metapneumovirus in China in December 2024, a cluster of unexplained deaths in Congo in February 2025.
How can you interpret these reports better? When is concern justified, and when is it not?
When a new disease outbreak makes headlines, most people fixate on the wrong details. They often focus on gruesome symptoms, reported deaths, and stories involving particularly sympathetic groups, such as young children.
The past two decades of pandemics – from SARS to Ebola to Covid-19 – have taught epidemiologists that it is more important to think about a potential outbreak across three dimensions. Was there laboratory confirmation? How easily does it spread? How severe is it? What tools do we have to prevent or treat it?
Was there laboratory confirmation?
When I trained in the Centers for Disease Control and Prevention’s Epidemic Intelligence Service, the first lesson we learned about outbreak response is: Confirm it’s an outbreak. Part of that involves comparing the number of cases against what is expected, but the other important part is testing specimens from ill persons.
Early reports may simply reflect clinical symptoms — cough, diarrhea, fever — not the actual cause. These reports often lack important details about what tests, if any, have been performed.
If the report describes people with respiratory symptoms, how many people had specimens collected? Were they from the nose, throat, or lungs? What about specimens from the blood (which can be important for some viral infections and invasive bacterial infections) or even from the urine (for Legionella)?
Was testing done using polymerase chain reaction, a highly sensitive method of identifying genetic fragments of pathogens, or were they done using other techniques? Were those tests done in high-quality (also known as “reference”) laboratories?
In many low-income countries, clinics may lack the supplies to collect certain specimens, hospital laboratories lack the ability to perform many advanced tests, and, even if those labs have the appropriate equipment, the quality of testing may be inferior. Much of my work in Southeast Asia on tuberculosis and in China on foodborne and respiratory infections involved trying to address these weaknesses.
To determine whether a disease is caused by a known pathogen or something truly new, investigators must perform extensive testing. Without it, a cluster of reports about people with vomiting and diarrhea could just as easily be due to norovirus or Salmonella as it could be a new pathogens.
Consider, for example, the Disease X “outbreak” from Congo in late 2024 involving (as of Dec. 16) 891 ill people and 48 deaths. For weeks, news outlets speculated that a new disease had emerged and could spread to other countries. After a large international response, testing of 420 samples identified “malaria, [as well as] common respiratory viruses (Influenza A (H1N1, pdm09), rhinoviruses, SARS-COV-2, Human coronaviruses, parainfluenza viruses, and Human Adenovirus).”
The presence — or absence — of laboratory confirmation helps separate signal from noise.
How easily does it spread?
The transmission patterns of a new disease provide crucial initial insights into its potential impact. The five most common routes of transmission are respiratory, vector-borne (e.g., mosquitos, ticks), direct contact, gastrointestinal, and body fluid (e.g., sexual, blood).
Of these, transmission by the respiratory tract is most worrisome. A person who expels a pathogen into the air by coughing or simply breathing (as happens with measles) can rapidly spread the infection to many people. When they do so in a public setting, they immediately extend the geographic spread of that pathogen beyond that person’s close contacts.
Think about how quickly the 2009 H1N1 influenza strain and Covid-19 spread around the world. This certainly explains why there was so much reporting about the increase in HMPV cases in China. But it’s important to put these infections in context. Unlike Covid-19, HMPV is a well-documented seasonal virus that has coexisted with human populations for decades. Understanding transmission requires looking beyond the simple fact of spread to examine whether a pathogen is following known patterns or exhibiting new behaviors.
Consider also the 2022 mpox outbreak. When it originally arose, there was concern that it might spread by the respiratory route similar to its sister virus, smallpox. But, to date, transmission appears limited to direct physical contact and the sexual route, which is why infections in the United States have largely been restricted to gay men and people in their sexual networks.
How severe is it?
Disease severity matters, but often not in the way that people think. Infections that kill a high percentage of people and that do so quickly can often be contained more easily than other infectious diseases. It is easy to identify and isolate the ill, and the ill have fewer opportunities to spread infections to other people.
Consider why Ebola never caused widespread outbreaks in the United States. People with Ebola are at highest risk of spreading infection when they are most severely ill – that is, they are not walking around, but rather confined to their bed or a hospital room.
Infections spread rapidly in settings in Africa, where infection control in health care facilities is inadequate, and where it is a common cultural practice for multiple people to bathe and touch a person after they have died – that is, at the moment of peak infectivity. Therefore, even though Ebola is a severe disease, those who are most severely ill in the United States are likely to be in a setting where they cannot readily spread the infection to others.
Consider also why SARS was contained, but Covid-19 has not been. With SARS, people did not readily spread the infection until they had symptoms. Even though those symptoms were severe (the “S” stands for severe), people could not readily spread it to other people because they were so ill.
Covid-19, in contrast, could infect people and not cause any symptoms. Many people cited this as a reason for why we should not be particularly worried about the virus. But, for infectious disease epidemiologists, this was one of its most worrisome features: People with minimal symptoms would walk around and spread it to lots of people without knowing it.
What tools exist?
Our capacity to respond to a disease threat represents the third crucial element in risk assessment. Do we have drugs that can reduce symptoms, reduce infectiousness, and/or cure disease? Do we have vaccines that can prevent severe illness and reduce infectiousness?
This is one reason Covid-19 was so problematic. When this pathogen emerged, we had no drugs or vaccines available and had to rely on masks and social distancing to reduce transmission. H5N1, bird flu, is particularly worrisome because existing influenza vaccines do not reliably prevent infection or reduce the severity of disease.
Thinking critically about outbreak news
In a world where information travels far faster than infections, it is more important than ever to think critically about reports of new diseases or outbreaks. While dramatic stories about individual cases may capture headlines, pay attention to both what these reports include and omit, particularly as it relates to laboratory testing, routes of transmission, disease severity, and existing treatments and vaccines. Evaluating the data behind the story is key to separating fear from fact.
Dr. Jay K. Varma is a physician and epidemiologist. An expert in the prevention and control of infectious diseases, he has led epidemic responses, developed global and national policies, and implemented large-scale programs that saved hundreds of thousands of lives in Asia, Africa, and the United States.
