Flu, COVID-19, and RSV... Possibility of Infectious Disease 'Quad-demic' Beyond 'Twin-demic' [News Terms]

The first death from avian influenza (H5N1) infection has occurred in the United States, and human metapneumovirus (HMPV) is spreading in countries such as China and India, raising global concerns about the possibility of a second COVID-19 pandemic. In South Korea, the number of flu and COVID-19 patients is increasing, raising fears of a "twindemic," while in the U.S., there is growing anxiety about a "quaddemic" with simultaneous outbreaks of flu, COVID-19, respiratory syncytial virus (RSV), and norovirus. Experts advise preparing for a "multidemic" situation where various infectious diseases occur simultaneously.

Yonhap News

According to the U.S. Centers for Disease Control and Prevention (CDC), at least 5.3 million flu cases have been reported nationwide this winter, with 63,000 hospitalizations. The number of deaths due to the flu is estimated to be around 2,700. Flu symptoms include systemic signs such as headache, fever, chills, and muscle aches, accompanied by respiratory symptoms like sore throat and cough. Some cases show respiratory symptoms without fever, similar to a cold, while others typically present with high fever and respiratory symptoms. Flu cases are also on the rise domestically. The Korea Disease Control and Prevention Agency (KDCA) reported that during the last week of last year (December 22?28), among 1,000 outpatients visiting 300 influenza sentinel surveillance medical institutions nationwide, 73.9 were suspected influenza cases, a roughly 2.4-fold increase from 31.3 the previous week.

COVID-19, which causes symptoms similar to the flu, is also expected to spread with a time lag. The Korea Medical Institute (KMI) forecasted this winter's respiratory infectious disease trends, stating that a "twindemic" of flu and COVID-19 could occur, making response measures important. According to the forecast, COVID-19 is expected to spread sequentially after the flu peak passes and students return to school. Over the past three years, flu and COVID-19 have tended to spread with a time lag, and in the past year, the dominant COVID-19 Omicron variants have shifted in the order of 'JN.1 → KP.2 → KP.3 → XEC.' The KDCA recommends vaccination before the Lunar New Year holiday, when many people travel and gather, as flu and COVID-19 cases are increasing.

In the U.S., concerns about a "quaddemic" are rising as cases of RSV and norovirus increase alongside flu and COVID-19. RSV is more common in infants and young children and causes symptoms similar to a cold, such as sneezing, nasal congestion, runny nose, sore throat, and fever. However, it can cause wheezing or rapid breathing and, in severe cases, pneumonia or respiratory distress. Norovirus, known as the "winter food poisoning," causes vomiting, diarrhea, chills, and fever. It spreads through contaminated water, seafood, or contact with infected individuals and is reportedly spreading faster than usual this year.

In countries like China and India, human metapneumovirus (HMPV), a respiratory infectious disease, is spreading. Although some have mentioned the possibility of an "HMPV pandemic," experts analyze that it is not a cause for concern like the COVID-19 pandemic. HMPV was first discovered in the Netherlands in 2001 and has been commonly referred to as a cold virus for decades, so it is not classified as a novel virus. HMPV mainly infects infants and young children, causing acute respiratory symptoms such as pneumonia and fever. In South Korea, patient numbers remain at average levels. The KDCA stated, "HMPV, which has recently been reported to increase overseas, is a common virus worldwide," and "No significant unusual trends related to HMPV have been observed domestically, with no large-scale outbreaks detected compared to average years." However, as the number of hospitalized patients has recently increased, they advise practicing basic respiratory infection prevention measures such as washing hands before and after going out, practicing proper cough etiquette, wearing masks when respiratory symptoms occur, and ventilating indoor spaces for more than 10 minutes every two hours.