Caught a flu? What You Should Know and What to Do

Written by Dr Sze Man WONG

 

Hong Kong has entered the winter seasonal flu as the circulation of influenza viruses in Hong Kong intensified. Outbreaks in schools and care homes have doubled in December to January , and hospital admissions are surging with the highest rate among children younger than 5. This winter, influenza will strike Kong hard, with the peak likely to be reached at the end of February. Thanks to its higher vaccination rates and experience from previous outbreaks, Hong Kong is better prepared to handle this seasonal challenge.  

 

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What is flu? Is it the same as the Common Cold?
What is flu? Is it the same as the Common Cold?

They are the same in a way that both are caused by viruses. The difference is that influenza viruses cause flu, while the common cold can be caused by different types of viruses, including rhinoviruses, parainfluenza, and seasonal coronavirus.

 

Influenza is an infectious disease caused by an enveloped RNA virus which mainly affects the upper respiratory tract (nose, throat, bronchi). There are 3 types of influenza viruses infecting humans: A, B and C 

  • Type A viruses are the more common form of the virus found in Hong Kong and they infect both humans and many animal species. Type A viruses are classified into subtypes denoted HxNy, based on their surface proteins, hemagglutinin (H) and neuraminidase (N). Currently, 2 subtypes circulate in the city: influenza A (H1N1)pdm09 and influenza A (H3N2).

  • Type B viruses infect almost exclusively humans. There are two lineages of type B viruses, B-Yamagata and B-Victoria.

  • Type C viruses cause generally mild illness. (which is not so common in HK)

 

What are the differences in Type A and B?

Influenza A: The Ever-Changing Virus

Type A and B viruses both are responsible for seasonal epidemics, but in most cases, influenza A causes pandemics. This is explained by the fact that influenza A mutates more quickly than influenza B. For the past years, most outbreaks of influenza are caused by the type A. The latest pandemic happened in 2009-2010 by the virus influenza A (H1N1), responsible for 280,000 deaths, which was the second historic pandemic caused by the H1N1 subtype.

 

Influenza B: The Human Flu

Unlike influenza A, influenza B viruses primarily circulate among humans. They cause seasonal flu outbreaks but generally result in milder symptoms than influenza A. However, severe cases and complications can still occur, especially in vulnerable populations.

 

What are the symptoms in Influenza Type A and Type B?

Symptoms in both appear between 1 and 4 days after contamination. The infection generally lasts a week and is characterized by the sudden onset of fever, muscle and joint pain, headache, tiredness and respiratory signs (dry cough, sore throat, rhinitis). Most affected patients recover within a week with symptomatic treatment (antipyretic, hydration, cough suppressant and rest).  

 

Certain fragile people are at risk of developing serious flu, which may require hospitalization in intensive care and the use of ventilatory assistance. People aged over 65, pregnant women, morbidly obese (body mass index or BMI >40 kg/m2), diabetics, immunocompromised people, people with chronic pathologies such as cardiovascular diseases or respiratory diseases, infants are at risk of developing complications and require greater medical attention.

 

Both influenza A and B are contagious but have similar symptoms. In general, influenza A is more commonly found at outbreaks and tends to circulate early in the season. Influenza A is more severe in adults, while influenza B is less common but can be severe than type A in children.

How is the infection transmitted?
How is the infection transmitted?

Influenza viruses are easily transmitted through microdroplets, and particles excreted by an infected patient when coughing, sneezing, or talking. They can also be transmitted through the hands when a person touches a contaminated surface and brings their hand close to the nose.  personal protection against the virus during epidemics is important. Cold temperatures favour the survival of influenza viruses, which explains, in part, why epidemics occur in winter in temperate climates.

How is the flu diagnosed?
How is the flu diagnosed?

An influenza test helps doctors to determine if you have the flu virus. Common types of flu tests are:

  • Rapid influenza diagnostic test: this is very commonly used at a doctor’s office. A sample is collected by nasal swab and tested for influenza antigens. This test takes about 15 minutes and helps to confirm the diagnosis and whether you have type A or B. The information about the strain of flu is important from a public health perspective, but it does not affect your treatment plan.

  • Rapid molecular assay: the sample is taken from a nasal swab and analyzed for its genetic profile.

  • Reverse-transcription polymerase chain reaction (RT-PCR): This flu test is the most accurate and can identify the subtype of the virus.
What are the treatments?
What are the treatments?

Both influenza A and B are treated in the same way. Fortunately, most people recovered from the flu on their own. Its treatment is mainly symptomatic by taking plenty of rest, staying well hydrated, being aware of red flags for complications and taking medicine to relieve cough and fever. Hygiene measures should be maintained to limit transmission.

 

Medications

The antiviral in Hong Kong are influenza neuraminidase inhibitors such as oseltamivir (Tamiflu®), which is active on both type A and B viruses. It works best if you take within 48 hours of the onset of symptoms. The usual course is 5 days, twice a day, and it can reduce the duration of the illness and the severity of symptoms if taken early.

How to prevent the flu?
How to prevent the flu?

During an epidemic, individual protection measures are necessary to avoid being infected or to transmit the virus. Wear a mask, use disposable tissues, wash your hands regularly, rest at home when you are sick… All these measures help to limit the virus’s spread in the city.

 

Annual flu vaccination, especially in fragile groups, remains the most effective way to protect yourself. Fortunately, the vaccine protects against both influenza A and B, and it helps to reduce serious forms of the flu, hospitalization, or even death. However, its protection lasts for 6 to 9 months as the influenza viruses modify its genetic material every year,requiring the composition of the vaccine to be adjusted. This is why a new flu vaccine with the most recent strains in circulation is introduced before each winter.

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