OK ladies, here's the deal. There are many, many infectious viruses, bacteria, and fungi that will cause flu-like symptoms in humans. Many of the viruses we tend to come in contact with on a "regular" basis, and which cause flu-like symptoms, are coronaviruses, parainfluenza virus, respiratory syncitial viruses, influenza viruses (A, B and C, and belong to the family Orthomyxoviridae), rhinovirus, norovirus, different types of herpesvirideae (like Epstein-Barr and cytomegalovirus), parvovirus (known better as slap cheek or 5th disease), all forms of hepatitis viruses and even HIV. This list is NOT inclusive -- there are many more types of infectious viruses, and many variant forms of each.
The primary cause of the symptoms is NOT the virus itself, but more often the body's own immune response to the virus (BTW, it is this same immune response that many people experience after receiving any kind of vaccination. This does NOT mean that the immunization has given you that disease). Thus, depending on the primary invasion point and individual susceptability, symptoms can be respiratory (cough, congestion, wheezing), gastrointestinal (nausea, cramping, diarrhea), dermal (rash, hives), neurological (pain, headache, malaise, numbness, and even minor or significant paralysis), and general (fever), or any combination. This is true for influenza as well as most of the other viruses.
So, SH is correct. You really can't diagnose true influenza by symptoms alone without an influenza test. One of the most common tests in use is the rapid test, which type of which can be done in doctor's office using a nasal swab. Most of these tests are looking for antibodies that are made against proteins the make up part of the viral packaging and can detect the presence of influenza A or B, but not C (which is much rarer, anyway). Some can only tell you if A or B are present, and some can tell you exactly which type of flu you're infected with. Unfortunately, this test can give a high rate of false negative results (that is, you are infected, but the test says that you're not), and will also give some false positive results (says you're infected, but you're actually not). There are also blood tests and culture tests that are more accurate, but can require more time to get a result.
Since, fortunately, this year the flu variants we're seeing are not as virulent as some we've seen in previous years, the flu is definitely uncomfortable and inconvenient, but not any more life-threatening than usual, although each year, influenza causes around 1/2 million deaths, worldwide. Thus, doctors recommend rest, fluids, and anti-inflammatory/anti-pyretic medications, such as ibuprofen, to help reduce aches and fever until the infection runs its course. The time to be concerned with influenza, is when an infected person begins to show signs of pneumonia or severe neurological symptoms, such as numbness and upwardly creeping paralysis (Guillan-Barre syndrome). Signs of viral pneumonia include extremely high fever (over 103 in children and over 101 in adults), wheezing and difficulty breathing (lungs will sound wet and raspy), and coughing up blood. Bacterial pneumonia is also a concern, as a secondary infection. Add to the above symptoms teeth-chattering chills, chest pain, rapid breathing, and rapid heart beat. If you or someone in your family has flu-like symptoms and then develops these other symptoms, this is a medical emergency, and you should seek help immediately.
This seems to be a particularly "bad" year in terms of flu infectiousness, although a fairly normal year in terms of seriousness. However, the more people who are infected by the virus, the greater the opportunity the virus has to "passage", and resurface in following years in a more severe form. (This is what happened in 1918, and part of what the CDC and the WHO were very concerned about with the 2009 H1N1 outbreak). The fewer people who are infected, the less opportunity the virus has to mutate into, potentially, a far nastier version, hence part of the drive to encourage people to get vaccinated. If you have not yet been vaccinated or have not had your children vaccinated, it is not too late to do so. Flu is more likely to be transmitted when the air is dry and humidity is low, such as in the early fall, late winter (if it's not raining a lot), and early spring.
Also, be aware that there is a particularly vicious strain of norovirus currently in circulation, which causes severe gastrointestinal symptoms (nausea, vomiting, diarrhea), and can lead to very rapid dehydration. The best way to protect yourself from this virus is to know who is handling your food (and make sure they're not sick), be cautious of what surfaces your food comes in contact with, and, as always, wash your hands well after using the restroom, coming in contact with common surfaces (light switches, door knobs) and preparing or eating food. Unlike influenza, which is airborne and transmitted in aerisolized particles generated by sneezing and coughing, norovirus is transmitted by the fecal-oral route.
BTW, for anyone who's interested in medical history or would like to get a better understanding of just how really dangerous influenza can be, I highly recommend John M. Barry's book "The Great Influenza." It is for the lay public and is extremely interesting.
