(NewsNation) — Mild sicknesses tend to spike during the winter months, but this season, public health experts are warning of a possible "quad-demic." The unofficial term "quad-demic" encompasses four infectious diseases: influenza, COVID-19, RSV, and norovirus. "We know that in certain areas of the country, they may have more activity of these viruses than others," Dr. Dana Hawkinson, the medical director of infection prevention and control at The University of Kansas Health System, told NewsNation. "Unfortunately, what we have seen recently in the last couple of weeks are increases in the rates of influenza infection throughout the country as well as COVID, which had been low after the summer peak. Now it is starting to increase as well." According to Dr. Hawkinson, some areas of the country are also seeing higher cases of norovirus. Add in whooping cough, walking pneumonia and bird flu, you may find yourself getting sick and unsure of how to distinguish among overlapping symptoms. Here's what to know. Flu Cases of influenza, or the flu, reached 40 million between 2023-2024, according to the Centers for Disease Control and Prevention. Symptoms include: Fever (some, not all) or feeling feverish/chills Cough Sore throat Runny or stuffy nose Muscle or body aches Headaches Fatigue (tiredness) Most people recover from the flu within days to a couple of weeks, but some cases can become severe. Last flu season, 28,000 people died, CDC data shows. COVID-19 COVID-19 has seemingly become a part of life just as the flu did. Cases are nowhere near as high as they were when the virus was first introduced, but the U.S. is still seeing positive tests, hospitalizations, and deaths. Between Oct. 1, 2024, and Dec. 14, 2024, the CDC estimates there were between 2.7 to nearly 5 million illnesses. Symptoms include: Fever or chills Cough Shortness of breath or difficulty breathing Sore throat Congestion or runny nose New loss of taste or smell Fatigue Muscle or body aches Headache Nausea or vomiting Diarrhea COVID-19 and flu symptoms are similar, but they are caused by different viruses. "You cannot tell the difference between flu and COVID-19 by symptoms alone because some of the symptoms are the same," according to the CDC. Anyone experiencing symptoms should take a COVID-19 test, either at a testing site, doctor's office or over-the-counter sold at pharmacies. The FDA previously granted approval for a combination flu and COVID test that can be used at home. RSV RSV, or respiratory syncytial virus, affects the nose, throat and lungs, usually peaking in December and January. Infants and older adults are most susceptible, Dr. Hawkinson notes. The symptoms are similar to the common cold and other respiratory infections like the flu and COVID-19: Runny nose Congestion Decrease in appetite Coughing Sneezing Fever Wheezing The CDC warns that not all symptoms will appear at once and may come in stages. Infants may experience only irritability, decreased activity, and breathing difficulties without the other symptoms. Sick season is in full force. What the latest CDC figures show RSV can cause other illnesses like bronchiolitis, which is inflammation of the lungs' small airways, and pneumonia. The CDC recommends RSV vaccines for those who are 75 years old and older, and for those as young as 60 who may be at an increased risk for severe RSV. If you received an RSV vaccine within the last year, you likely don't need another shot this year, Dr. Hawkinson says. Norovirus The stomach bug is striking again. Norovirus is highly contagious, spread through contact, and causes inflammation of the stomach and intestines. The CDC reports about 19 to 21 million annual cases. People of all ages can get norovirus, but more severe infections occur in children younger than five years old, older adults and people with weakened immune systems. Symptoms typically develop within 12-48 hours of exposure. They include: Diarrhea Vomiting Nausea Stomach pain Fever Headache Body aches Dehydration Other illnesses to watch this winter Bird flu, walking pneumonia and whooping cough are also on doctors' radars. An outbreak of bird flu, or H51N avian influenza, popped up in poultry and dairy cows. The disease is common in wild birds worldwide, but it was recently diagnosed in humans. The CDC confirmed 66 reported cases in the U.S. since last April, detecting the first severe human case in Louisiana on Dec. 13. Infected people may not experience any symptoms, but if they do, symptoms can include an eye infection on the mild side to pneumonia and death in more severe instances. No person-to-person spread has occurred, according to the CDC. Atypical, or walking, pneumonia is a mild lung infection that can develop from bacteria, viruses or mold. Its name comes from the idea that people often don't know they have it and can carry on with daily activities despite the symptoms. Typically, those who become ill do not require hospitalization, which can often happen with severe cases of pneumonia. The CDC reports about two million infections each year, with cases increasing in the later months of last year. Symptoms, similar to those in a bad common cold or the flu, include: Sore throat Fatigue Chest pain or discomfort Low-grade fever (less than 101 degrees Fahrenheit or 38 degrees Celsius) Mild chills Cough Sneezing Headache Lastly, whooping cough, also known as pertussis, is especially concerning for children who are too young to have completed vaccinations. The highly contagious respiratory tract infection causes a severe hacking cough, following by a "whoop" sound with an intake of breath, according to the Mayo Clinic. More than 10,000 cases are reported annually, according to the CDC. Symptoms, which begin about five to 10 days after exposure and occur in stages, include: Runny or stuffed-up nose Low-grade fever (less than 100.4°F) Mild occasional cough Vomiting during or after coughing fits Fatigue in between coughs Difficulty sleeping Struggle to breathe There are different whooping cough vaccines depending on your stage of life. For young children, doses are typically administered two, four, and six months after birth, as well as 15 to 18 months after and between the ages of 4 and 6 years old. Children get another dose when they are 11 or 12 years old. Women who are pregnant are able to get the whooping cough vaccine during the 27th to 36th week of each pregnancy. Adults are able to receive a vaccine at any time if they have never received it. If you are sick for several days or are experiencing severe symptoms, like longlasting diarrhea that can lead to dehydration, Dr. Hawkinson recommends seeking medical care. The Associated Press contributed to this report. Latest News Stray dog shot in the face gets a new lease on life in Denver Louisiana AG orders security review after New Year’s Day truck attack in New Orleans Trump critic named new Washington archbishop Southern University basketball team opens SWAC play with win over Texas Southern What to expect from gas prices in 2025