No, the stomach “flu” isn’t related to influenza – but it does appear to be surging across the United States and United Kingdom . According to data from the Centers for Disease Control and Prevention (CDC), positive tests for norovirus are at a 12-month high as of March 2023 . Norovirus is a highly contagious virus that packs a mean punch and can cause vomiting, diarrhea, fever and chills. In some regions, the current outbreak has forced schools to close and even overtaken cruise ships.
However, norovirus is far from the only gastrointestinal pathogen that is cause for concern. During a recent webinar, Davidson Hamer, MD, Professor of Global Health and Medicine at the Boston University School of Public Health, shared an overview of the many potential causes of infectious gastroenteritis and why molecular testing is critical to help differentiate.
Too many pathogens, too little time
According to Dr. Hamer, infectious gastroenteritis is a disease in which a person’s small and/or large intestine becomes severely inflamed, leading to diarrhea. Infectious gastroenteritis can be caused by bacteria, viral or parasitic pathogens, and, rarely, fungal pathogens. Depending on the cause of infection and severity of diarrhea, infectious gastroenteritis can result in complications, including dehydration, significant weight loss, kidney damage, hypoglycemia and more.
“There’s a long history of diarrhea. Honestly, this has been around for millennia,” said Dr. Hamer. Experts first suspected that viruses were related to diarrhea around 1901. Norovirus itself was known as the “Norwalk virus” until 1990, after being discovered as the cause of an outbreak in Norwalk, Ohio in the 1960s. Today, more than 20 pathogens have been identified to cause infectious gastroenteritis, with salmonella, shigella, Vibrio cholerae, C. difficile, E-coli, rotavirus, noroviruses and Giardia lamblia as some of the leading causes.
Not only are there many potential pathogenic causes of infectious gastroenteritis, explained Dr. Hamer, but there are many potential vehicles for transmission. Some infections may be spread from person to person while others may be spread via contamination through food, water or surfaces.
Identifying the culprits through enteric testing
Diarrheal disease is one of the top ten causes of death globally, with deaths significantly more common in developing countries . Dr. Hamer shared that in the United States alone, approximately 300 children die each year from infectious gastroenteritis. With so many gastrointestinal pathogens circulating, enteric pathogen testing can help identify what’s causing disease.
“From an epidemiology standpoint, it’s important to understand what are the major causes, what’s the evolution and [what are the] changes, but also to be able to identify outbreaks,” said Dr. Hamer, “What do they have? Is it bacterial? Is it an invasive diarrhea that needs antibiotics? What is the antibiotic susceptibility pattern? Or is this something like norovirus where we have no treatments but need to know that there might be an outbreak or that there’s a risk of an outbreak at home?”
Fortunately, there are several different test and specimen options for identifying diarrhea-causing pathogens. Stool is typically the preferred clinical specimen for diagnosis, explained Dr. Hamer, but vomit and serum can be utilized for certain research. Over the years, testing has improved – from cultures that can take days to molecular testing using polymerase chain reaction (PCR) that can deliver results in a few hours.
PCR testing as a preferred method for pathogen detection
As an infectious disease physician, Dr. Hamer shared that molecular testing with PCR has proven helpful in identifying the cause of patients’ diarrhea more quickly than other test types. However, according to Dr. Hamer, the benefits of molecular stool testing for infectious gastroenteritis go beyond the rapid turnaround time. These tests offer higher sensitivity and specificity, can detect multiple pathogens with one sample, and can also help in identifying coinfections.
“This is a really fantastic revolution, so much has happened in the last 10-15 years, but it just amazes me how many hospitals now have multiplex assays to test for GI pathogens,” said Dr. Hamer. He went on to explain the differences between broad molecular panels, which can cover more than 20 potential pathogens, and multiplex panels. Broad panels may be used in critical cases, for example with a hospitalized patient, where detecting the cause quickly to enable treatment is critical. On the other hand, multiplex panels are more cost-effective and are often used in outpatient environments where providers may choose to order specific panels based on clinical presentation.
Dr. Hamer shared the success story of one patient who, based on recent travel to India and clinical presentation, initially appeared to have traveler’s diarrhea. However, molecular testing revealed this patient was actually suffering from norovirus, which had spread during a family gathering the day after the patient returned from travel. “This just shows one example of how testing can be used and sometimes leads to surprising results,” concluded Dr. Hamer.
To learn more about potential causes of infectious gastroenteritis and how to detect specific pathogens using molecular testing, watch the webinar on-demand.
For more information on gastrointestinal pathogens, please visit this page. https://www.thermofisher.com/us/en/home/clinical/clinical-genomics/molecular-diagnostics/gastrointestinal-diseases.html.
- New Scientist | Norovirus outbreak: Why is the number of cases in England so high?
- Centers for Disease Control and Prevention | Norovirus National Trends
- World Health Organization | The top 10 causes of death