Diagnosis
Differentiating between a cold and flu may be difficult. Cold symptoms are nearly always less severe than those of the flu.
Comparing Colds and Flus
Symptoms | Cold | Flu |
Fever | Rare | Common and high (102-104° F); lasts 3 - 4 days |
Headache | Rare | Almost always present |
General aches and pains | Mild, if they occur at all | Often severe |
Fatigue, exhaustion, and weakness | Mild, it they occur at all | Extreme exhaustion is early and severe; can last 2 - 3 weeks |
Stuffy nose | Nearly always | Sometimes |
Sneezing | Very common | Sometimes |
Sore throat | Common | Sometimes |
Chest discomfort and cough | Mild to moderate, hacking cough | Common, can be severe |
Source: National Institute of Allergy and Infectious Disease | ||
Diagnosing the Flu
Several available tests can isolate and identify the viruses responsible for some respiratory infections. They are generally not needed, since most cases of the flu are self-evident. However, such tests can be very helpful in confirming or ruling out the flu. If a doctor believes a diagnosis would help, samples using a swab should be taken from the nasal passages or throat within 4 days of the first symptoms.
Several rapid tests for the flu can produce results in less than 30 minutes, but vary on the specific strain or strains that they can detect. They are not as accurate as a viral culture, however, in which the virus is reproduced in the laboratory. Culture results can take 3 - 10 days. Blood tests can also document the infection several weeks after symptoms appear.
Diagnosing Avian Influenza
In February 2006, the U.S. Food and Drug Administration approved a new, faster test for diagnosing strains of avian influenza (bird flu) in people suspected of having the virus. The test is called the Influenza A/H5 (Asian lineage) Virus Real-time RT-PCR Primer and Probe Set. The test gives preliminary results within 4 hours. Older tests required 2 - 3 days.
Ruling out Other Causes of Congestion
Ruling out Allergic Rhinitis. Symptoms of allergic rhinitis include nasal obstruction and congestion, which are similar to the symptoms of a cold. People with allergies, however, are likely to have the following:
- Thin, clear, and runny nasal discharge
- An itchy nose, eyes, or throat
- Recurrent sneezing
There are two forms of allergic rhinitis:
- Symptoms that appear only during allergy season are called allergic rhinitis, commonly known as hay or rose fever. [For more information see In-Depth Report #77: Allergic rhinitis.]
- Allergens in the house, such as house dust mites, molds, and pet dander, can cause year-long allergic rhinitis, referred to as perennial rhinitis.
Click the icon to see an image of common allergens.
Ruling out Sinusitis. The signs and symptoms suggestive of true acute sinusitis include the following:
- A return of congestion and discomfort after initial improvement in a cold (called double sickening)
- Purulent (pus-filled) nasal secretion
- A lack of response to decongestant or antihistamine
- Pain in the upper teeth or pain on one side of the head
- Pain above or below both eyes when leaning over
Children with sinusitis are less likely to have facial pain and headache and may only develop a high fever or prolonged upper respiratory symptoms (such as a daytime cough that does not improve for 11 - 14 days). When the diagnosis is unclear or complications are suspected, further tests may be required. [For more information see In-Depth Report #62: Sinusitis.]
Ruling Out Other Causes of Coughing
Acute Bronchitis. Acute bronchitis is usually caused by a virus and in most cases is self-limiting. The cough it causes typically lasts for about 7 - 10 days, but in about half of patients, coughing can last for up to 3 weeks, and 25% of patients continue to cough for over 1 month.
Atypical Pneumonia. Pneumonia caused by atypical organisms (for example, Mycoplasma pneumonia, Legionella) can cause symptoms similar to the flu. Only laboratory tests can diagnose the difference. [For more information see In-Depth Report #64: Pneumonia.]
Ruling out More Serious Viral Infections. Respiratory syncytial virus (RSV) and, possibly human parainfluenza viruses (HPV), are proving to be important causes of serious respiratory infections in infants, the elderly, and people with damaged immune systems. (Both also cause mild conditions.) RSV may be a much more common cause of flu-like symptoms than previously thought. In one British study of patients with flu symptoms, RSV was responsible for 22% of the cases and influenza for 32%. And among children under age 5, RSV was responsible for more flu-like cases than the flu virus itself.
Pertussis. Pertussis (whooping cough) was a very common childhood illness throughout the first half of the century. Although immunizations caused a decline in cases to only 1,700 in the U.S. in 1980, the incidence has risen recently, with almost 30,000 cases reported between 1997 and 2000 (17 infants died of the disease in 2000). Many more cases are reported worldwide.
Nearly half of pertussis cases now occur in people 10 years of age or older, perhaps due to waning immunity in adolescents and adults. Such cases may be greatly underreported. One study suggested that as many as 25% of adults who see a doctor for persistent cough may actually have pertussis. It may go undiagnosed, however, because symptoms are usually mild, and adults are unlikely to have the classic "whooping" cough. This is of some concern because such adults may unknowingly infect unvaccinated children. The younger the patient, the higher the risk for severe complications, including pneumonia, seizures, and even death. Children younger than 6 months are at particular risk because protection is incomplete, even with vaccination.
Ruling Out Other Causes of Sore Throat
In addition to common cold viruses, other, less frequent causes of sore throat include the following:
- Strep throat
- Sore throat related to the flu
- Foodborne and waterborne infections (Streptococcus C and G)
- An uncommon organism called Arcanobacterium haemolyticum (infection with this bacterium can mimic strep throat and may even cause a rash)
- Infectious mononucleosis ("mono")
- Herpesvirus 1
- Pneumonias caused by the atypical organisms mycoplasma or chlamydia
What is Strep Throat?Group A Streptococcal bacteria is the most common bacterial cause of the severe sore throat known commonly as "strep throat." It occurs mostly in school age children, but people of all ages are susceptible. (Strep throat constitutes only about 12% of all sore throat cases seen by doctors.) The symptoms of strep throat include the following:
Only about half of patients with strep throat have such clear-cut symptoms. Furthermore, half of people who have these symptoms do not actually have strep throat. How Is Strep Throat Diagnosed? Most cold-related sore throats are caused by viruses and require no treatment. They usually do not last more than a day. When the sore throat persists and is very painful the doctor will want to rule out or confirm the presence of the strep bacteria.
A throat culture is the most effective and least expensive test for confirming the presence of strep throat. It takes 24 - 48 hours to obtain a result. Rapid Antigen-Detection Test for Strep Throat. A faster test called the rapid strep antigen test uses chemicals to detect the presence of bacteria in a few minutes. A positive result nearly always means that streptococcal bacteria is the cause of the infection. The test, however, fails to detect between 10 - 20% of cases, so a culture may still be necessary to catch any missed infections, particularly in children. How Serious is Strep Throat? The use of antibiotics has removed the threat of most complications from streptococcus infection in the throat (strep throat). However, untreated strep throat could lead to the following complications:
How Is Strep Throat Treated? Strep throat infections require antibiotics. The following are generally used:
Antibiotics are very commonly inappropriately prescribed for non-Strep sore throats. One study reported that an estimated 6.7 million American adults visited their doctors because of sore throat between 1989 and 1999, with 73% of them receiving antibiotics. Studies indicate, however, that less than half of adults and far fewer children with even strong signs and symptoms for strep throat actually have strep infections. Parents should be comforted that a delay in antibiotic treatment while waiting for lab results does not increase the risk that the child will develop serious long-term complications, including acute rheumatic fever. If a patient is severely ill, however, it is reasonable to begin administering antibiotics before the results are back. If the culture is negative (there is no evidence of bacteria), then the doctor should call the family to make certain they stop taking the antibiotics and discard any remaining pills. |
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