Dr Rajiv Desai

THE SWINE FLU

January 23, 2010 by Dr Rajiv Desai

 

NOVEL H1N1 INFLUENZA OF THE YEAR 2009 (Misnomer- Swine Flu)

Prologue: I never wanted to write on this subject because information is readily available on TV but as usual, Media is creating panic in the mind of people by showing every death as breaking news.

Abbreviation used: Novel H1N1 influenza = H1N1 flu = HNF

   Let us start with number of deaths per year due to various infectious diseases in the world.

Infectious disease   deaths in millions

Pneumonia            4.18

Diarrhea                 2.16

HIV                       2.08

TB                         1.46

Malaria                   1.3

Seasonal flu          0.5

HNF                      0.002

People can see that there is no comparison between deaths due to other infectious diseases and HNF.

However, HNF is a caused by a new virus and therefore people do not have immunity against it and so some amount of concern is acceptable but the virus is having low virulence .However, winter is a season of flu and second attack by this virus in winter could be more severe because virus may undergo mutation.

Acute viral respiratory illnesses account for more than 50 % of all acute illnesses. The incidence is 3 to 5 illnesses per person per year. 75 % of all acute respiratory illnesses are viral in origin. These viruses are rhino virus, corona virus, adeno virus, respiratory syncytial virus, influenza virus etc.

Influenza virus is an enveloped RNA virus having 3 types A, B and C. It affects humans, pigs and birds. Influenza A virus is subdivided on the basis of surface Haemagglutinin (H) and Neuraminidase (N). H are of 15 subtypes (H1 to H15) and N are of 9 subtypes (N1 to N9).  All subtypes are found in birds and birds are the primordial reservoir of influenza A viruses. HNF is H1N1.

The swine flu influenza virus is also H1N1 type and affects pigs causing flu epidemic in pigs. Experts believe that HNF virus first originated in pigs in Asia and migrated to North America by humans and has now become a human virus and hence it is called swine-origin human H1N1 influenza A virus.

Swine flu H1N1 virus, Human seasonal flu H1N1 virus and novel H1N1 virus are different from each other and therefore swine flu H1N1 vaccine/ seasonal flu H1N1 vaccine are useless for novel H1N1 virus.

Concept of Antigenic shift/drift:

Influenza type A virus has segmented genome of RNA and not single strand of RNA. It has 8 segments of RNA in it. When swine flu virus and human flu virus  simultaneously invade the pig respiratory cell, the host cell acquire 16 segments of RNA and by chance, if 4 swine flu RNA segments and 4 human flu RNA segments combine to form a virus, then, it will be a new (reassorted) flu virus by the process of antigenic shift. During antigenic drift, the flu virus maintains same 8 RNA segments but with small changes.

Every year influenza outbreaks occur in humans/animals/birds but pandemic in humans occur every 10 to 15 years. During pandemic of 1918-1919, more than 40 million people died. Every pandemic affects 10 to 20 % of world’s population.

HNF is a novel H1N1 influenza A virus causing acute respiratory illness, first detected in January 2009 in Mexico city and spread worldwide through international airlines. WHO declared it as pandemic on 11 June 2009. Pandemic is defined by how fast the new flu virus spread and not necessarily by the severity of the illness. The illness appears to be mild in 99 % of the patients. By august 13, 2009; total number of laboratory confirmed cases of HNF is 182166 and total deaths 1799 in 177 countries of the  world .However, millions are infected with mild disease who did not undergo virus testing or who had clinically unapparent illness. 71% of all influenza viruses circulating in the world are novel H1N1 virus and therefore routine virus testing is no longer necessary as patients with flu-like symptoms most likely have it.

HNF has incubation period of 1 to 4 days and illness last for 7 days in most patients except severe/complicated cases. HNF is highly contagious even before the patient gets symptoms and during illness. The reproduction ratio(number of secondary cases from the primary case) for novel H1N1 virus was 2.2 to 3.1 in Mexico which is more than reproduction ratio of 1918 H1N1 influenza virus.

HNF spreads from one human to another by droplet nuclei which are generated during coughing/sneezing/talking. Droplet nuclei are conglomeration of moisture and viruses and it has the diameter of 1 micron to 5 microns and remains suspended in air for several hours. One cough generates 3000 droplet nuclei and even 5 minute talk generates 3000 droplet nuclei. One Sneeze generates 10000 droplet nuclei which travel at the speed of 5oo km/hour up to 10 feet. When the droplet nuclei enter the nose/throat of a healthy person, he can get infected. The virus can survive for 8 to 12 hours on environmental surface like mask, hand, table, door, books etc. When such a virus-containing contaminated surface touches nose/mouth of a healthy person, the person gets infected.

N 95 mask (respirator) blocks 95 % particles of size more than 0.3 microns and therefore blocks droplet nuclei. However, the diameter of virus is 0.1 microns. When a healthy person wears N95 mask, the droplet nuclei from the infected person will be blocked but after few hours, when the moisture of droplet nuclei evaporates, the free viruses are liberated which can enter through N 95 mask due to negative pressure generated during every breadth as mask snugly fits on the face.. So N 95 mask is good to protect people when worn by the patient but not so good for self-protection when worn by the healthy person.

Clinical feature of HNF is abrupt onset fever, cough, sore throat, running nose, vomiting, diarrhea etc.

Two groups deserve special attention and may need hospitalization.

Group 1)  High risk persons who are more susceptible to infection than normal includes children, elderly, pregnant women, patients having asthma/COPD, heart disease, diabetes, kidney failure, HIV, immune-compromised, cancer etc.

Group 2) Healthy persons having severe disease manifested in adults as breathlessness, coughing of blood, shock, drowsiness etc and in children as difficult breathing, not eating/drinking, unresponsive etc.

Diagnosis is made by sending naso-pharyngeal/throat swab to laboratory where real time Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) is done. RT-PCR positive means patient infected with HNF. The Rapid Influenza antigen test has 51% sensitivity and 99 % specificity for novel H1N1 virus which means chances of false negative are high. Other methods are viral culture and 4 fold rise in specific neutralizing anti-H1N1 antibodies.

How to prevent spread of HNF:

1)      Cover mouth/nose with tissue/handkerchief at the time of coughing/sneezing/talking.

2)      Wash hands frequently with soap and water especially after coughing/sneezing.

3)      Confirmed/suspect cases must wear N 95 masks.

4)      Keep distance of 6 feet away from confirm/suspect cases.

5)      Avoid crowded places.

6)      Do not visit hospital/clinic unnecessarily.

7)      If you have symptoms of flu, take 7 days rest at home and do not attend school/factory/office at that time.

8)      Avoid touching mouth/nose/eyes with hand.

9)      Keep windows open and use fan instead of AC.  Only AC with HEPA filters are allowed as it traps droplet nuclei.

School closure does not help because the virus spread very fast and by the time decision is taken to close school after an index case, students are already infected. The sick student must not attend school until 24 hours after all symptoms have subsided.

 Influenza virus is killed by heat, soap, chlorine/iodine, hydrogen peroxide, alcohol etc.

There is no point wearing mask by ordinary people on the streets. It creates panic.

Treatment of HNF is Oseltamivir (tamiflu) and Zanamavir (Relenza).  The drug is useful if taken with in 2 days of the onset of illness. It reduces duration and severity of illness. After 2 days, its use is doubtful. Most mild cases do not need it and when severe complication occurs, it is too late for the drug to be effective.

The cause of death in severe cases of HNF is pneumonia, either viral pneumonia occurring within 2 days of onset of illness or bacterial pneumonia occurring 7 days after onset of illness or both.

‘ The best way to prevent death is to detect pneumonia early and treat it fast.’

HNF produces immune response in which cytokines like C – reactive protein (CRP), Interleukin 6, Tumor necrosis factor Alfa etc are released and severe the infection, greater is the release of cytokines. . CRP level in blood can be measured in any small lab. Oxygen saturation in blood is reduced in pneumonia which can be measured even in small clinic. X-ray of chest can detect pneumonia even before patient is breathless and must be done on 2’nd day and anytime when patient is breathless. X-ray is available in any small town.  So this triad of CRP level, blood oxygen saturation and chest X-ray can detect severe HNF cases even in small town where RT-PCR is not available. If anybody is afraid of death after flu-like symptoms, do not rush for viral testing but get this triad done in your town and if normal, you are not going to die even if you may be having HNF.

Novel H1N1 vaccine will be available in near future to prevent infection but may become ineffective if virus undergoes mutation or another new virus comes up.

THE MORAL OF THE STORY:

1)      Best way to prevent H1N1 flu is good personal hygiene and health education. Every child must be taught by parents/teachers to cover mouth/nose at the time of coughing/sneezing.

2)      Best way to prevent death in H1N1 flu is early detection of pneumonia by triad of CRP level, oxygen saturation level in blood and chest X-ray; which are available in any small town.

3)      Oseltamivir (tamiflu) has a very limited role in saving lives.

4)      Panic does not help but harm everybody.

Dr.Rajiv Desai. MD.