Flu is the short term for influenza. When we sneeze or cough, then we can spread this viral infection if we are affected from it. When we have this kind of infection, then we feel uncomfortable. This infection will get better in a period of one week. In every part of the year we can be affected with flu. But this infection is most common in the winter.  This infection is known as seasonal flu. But there is difference between flu and common cold. They are not the same condition. When you have flu, then this kind of infection is not caused by the same group of viruses which are causing the common cold. When you have flu, then they can start suddenly. Also they can last longer than the symptoms of the common cold and they are more severe.
When someone is infected with this infection, then the symptoms of it are developing from one to three days. When you are infected from this disease, then usually it gets better after one week. But also there are some cases when you are affected with this disease and you feel very tired or you have a lingering cough after there have passed couple of weeks. Here are the most common symptoms of flu :
- A sudden fever – a temperature of 100.4 F (38 C) or above
- Difficulty sleeping
- A dry and chesty cough
- Loss of appetite
- A headache
- A runny or blocked nose
- Tiredness and weakness
- A sore throat
- Nausea and vomiting
- Aching muscles
- Diarrhea or abdominal (tummy) pain
- Limb or joint pain
There are some cases when it is very difficult to tell if you suffer from cold or flu. Symptoms of the both diseases can be very similar. But also they have some differences such as
- Flu symptoms: You feel unwell which means that you cannot do the everyday activities. You have aching muscles or fever. The symptoms of the flu come in very quick way.
- Cold symptoms: The symptoms of this condition are coming gradually. In the most cases they are affecting the throat and nose. The symptoms of this condition are mild symptoms. This means that you are not all day long in your bed and you can do the everyday activities such as go to work, school, college etc.
Complications of flu: People who are in their older ages, people who have weak immune system, people who take medications in long period and pregnant women are having the biggest chances to get complications from flu.  If you are in the mentioned groups, then you must take your annual flu vaccination. Also you must visit your doctor as soon as possible if you have the mentioned symptoms of flu.
- Chest infections: Bronchitis is a type of chest infection. It is one of the most common complications of the flu. In some cases they can develop into pneumonia which is dangerous disease. There are antibiotics which are used from pneumonia treatment but elderly and frail people are risking having life – threatening condition. 
- Worsening of existing conditions: If someone has life – threatening condition, then if they get flu they are risking having worsening of their condition. People with chronic obstructive pulmonary disease and asthma if they get flu, then they can notice that they symptoms of their disease are more severe than before. This disease also can affect diabetic people. It can cause them hyperglycaemia which means that they will have high blood sugar levels. People who suffer from diabetes type 1 and who get flu this condition can worsen their disease into diabetic ketoacidosis which is very serious and dangerous disease caused by lack of insulin in their bodies. If you suffer from some type of diabetes (types 1 and 2) and if you take insulin, then you should constantly monitor your blood sugar levels. 
- Pregnancy complications: If you are pregnant and you have flu, then you are under risk to get some complications. This infection can cause your baby to have low weight when it is born or it can result in premature labour. Also there are some cases when the flu in the pregnancy has resulted in a stillbirth or miscarriage. 
- Rare complications such as meningitis, tonsillitis, sinusitis, encephalitis, otitis media and febrile seizures convulsions.
These are some conditions of the Flu.
 Harvard University. The reason for the season: why flu strikes in winter. 2014. Retrieved from sitn.hms.harvard.edu/flash/2014/the-reason-for-the-season-why-flu-strikes-in-winter/
 Centers for Disease Control and Prevention (CDC). Clinical signs and symptoms of influenza. Retrieved from www.cdc.gov/flu/professionals/acip/clinical.htm
 Bidwell A. Weaker immune systems make men more vulnerable to the flu. U.S. News. 2013. Retrieved from www.usnews.com/news/articles/2013/12/23/weaker-immune-systems-make-men-more-vulnerable-to-the-flu
 American Lung Association. Learn about acute bronchitis. Retrieved from www.lung.org/lung-health-diseases/lung-disease-lookup/bronchitis/learn-about-bronchitis
 den Akker IL, Verheij TJM, Buskens E, et al. Clinical effectiveness of first and repeat influenza vaccination in adult and elderly diabetic patients. Diabetes Care. 2006;29(8):1771-6.
 RMIT University. New study reveals why flu can be devastating for pregnant women: Pre-clinical study suggests virus does not stay in the lungs but spreads throughout the mother’s body. Science Daily. 2020. Retrieved from www.sciencedaily.com/releases/2020/09/200921151321.htm