Differentiating Viral Infections

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Infectious Disease: Differentiating Viral Infections 

Several viral outbreaks are spreading across the United States (US), including norovirus, avian flu, influenza, and respiratory syncytial virus (RSV). Norovirus, also known as the Cruise Ship virus due to cruise ship outbreaks, is the leading cause of foodborne illness in the US. However, despite this name, 62% and 22% of cases originate from health care facilities or restaurants, respectively. This 2025's New Year's week saw a notable rise in positive tests compared to last year’s peak season (28% vs 13.52%). Current rates have met or exceeded last season’s peak numbers in all regions of the country, with the highest rates in the Midwest from Kansas to Michigan. Although mortality risk is low for most patients, more severe cases may result in dehydration or renal failure. [1] 

Avian flu, or Bird flu, originate from infected wild birds or poultry and mainly affect regions with dairy and poultry industries, like California, Washington, and Colorado. The public health risk is low, with only one confirmed death. However, due to limited data on treatment and prevention, and the flu's higher potency and longer duration, the US Center for Disease Control and Prevention (CDC) continues to monitor for changes in public risk. [2] 

As of January 2025, the influenza season has led to 16 million cases, 190,000 hospitalizations, and 8,300 deaths. With flu season lasting until May, these numbers may continue to rise. However, current rates have led to preventative measures, such as periodical school closured in Texas, Ohio, Oklahoma, Georgia, Virginia, and Tennessee, due to over 57 pediatric flu-related deaths. [3,4] 

Respiratory syncytial virus (RSV) is characterized by mild, cold-like symptoms with wheezing, impacting infant and geriatric populations disproportionately. From October 2024 to February 2025, the CDC estimated 2.1 to 4.3 million outpatient visits, 110,000 to 230,000 hospitalizations, and 5,700 to 14,000 deaths. However, accurate RSV data is difficult to gather, as the RSV Hospitalization Surveillance Network only includes hospitals serving 8% of the U.S. population, and many RSV cases go untreated. [5] 

COVID-19, the SARS-CoV-2 coronavirus responsible for the 2019 global pandemic, still remains in circulation. An estimated 6–10.8 million COVID-19 cases have occurred from October 2024 to January 2025, resulting in 19,000-34,000 deaths. Due to the influx of COVID-19, norovirus, RSV, and influenza cases, experts have coined the term “quad-demic,” highlighting the increased risk of multiple community-acquired infections. As risk factors overlap, especially between respiratory infections, certain patients may have a greater risk of simultaneous respiratory illnesses. See Table 1 for differentiated characteristics of these microbes. [6] 

Table 1:

 

Seasonal flu, RSV, and COVID-19 carry great risk of respiratory impact, especially in at-risk populations like infants who lack an available RSV vaccine. Moderna has made a previous attempt for RSV vaccine development; however their study was halted due to the increased incidence of severe respiratory illness. Currently, Moderna is collecting information in this population, with the intention of driving future innovations for RSV prevention. Although treatment for avian flu overlaps with seasonal flu, data supporting the use of neuraminidase inhibitors (i.e., oseltamivir, baloxavir) for Bird flu is limited. Meanwhile, norovirus is lacking in both treatment and vaccine research, with data simply supporting supportive care and vigilance in high-risk settings like daycares, cruise ships, or nursing homes. In general, experts advise preventative care such as adherence to food hygiene practices, and administering available vaccines (i.e., influenza and RSV) to reduce the risk of co-infection. [6-8] 

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References: 

[1] Tin A. Norovirus wave now more than double last year’s peak, in CDC’s data. CBS News. Published January 14, 2025. https://www.cbsnews.com/news/norovirus-wave-twice-last-year-cdc-data/ 

[2] Highly pathogenic Avian influenza A(H5N1) virus: Interim recommendations for prevention, monitoring, and public health investigations. Avian Influenza (Bird Flu). Published December 26, 2024. https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html 

[3] Flu outbreak causes school closings across the country. TODAY.com. Published online February 7, 2025. https://www.today.com/health/cold-flu/flu-school-closures-2025-rcna190771 

[4] Weekly US Influenza Surveillance Report: Key Updates for Week 3, ending January 18, 2025. FluView. Published January 27, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-03.html 

[5] Cohen J. ‘Safety signal’ in Moderna’s RSV vaccine studies halts trials of other vaccines for childhood killer. Science | AAAS. https://www.science.org/content/article/safety-signal-moderna-s-rsv-vaccine-studies-halts-trials-other-vaccines-childhood. Published December 13, 2024. 

[6] CDC. COVID Data Tracker. Centers for Disease Control and Prevention. Published March 28, 2020. https://covid.cdc.gov/covid-data-tracker/#datatracker-home 

[7] Prevention and antiviral treatment of avian influenza A viruses in people. Avian Influenza (Bird Flu). Published July 19, 2024. https://www.cdc.gov/bird-flu/prevention/index.html 

[8] Interim Guidance on the Use of Antiviral Medications for Treatment of Human Infections with Novel Influenza A Viruses Associated with Severe Human Disease. Avian Influenza (Bird Flu). Published September 12, 2024. https://www.cdc.gov/bird-flu/hcp/novel-av-treatment-guidance/ 

 

 

 

 

 

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