Swine flu

Key facts:

Author: Dr Judith Timms
Top Tip: Don't admit, unless necessary 

Key Differential Diagnoses

• Other forms influenza
• Other viral and bacterial illnesses

Key Investigations

• Nose and throat swabs (if necessary, according to local protocols). If admitted, also:
• FBC, CRP, ESR
• U+E, LFT, Bone, Glucose
• BC
• CXR (if necessary, eg to exclude other diagnoses; do not let wander around dept)

Key Treatment

• PO OSELTAMIVIR (Tamiflu) 75 mg bd or PO ZANAMIVIR (Relenza) 10 mg bd, both 5 days

Key Management Decisions

• Treat/not (senior decision)
• Admit/not (senior decision)
• Isolate suspected patient, and wear PPE

Background

On June 11, 2009, the World Health Organization (WHO) raised the worldwide pandemic alert level to Phase 6 in response to the ongoing global spread of the novel influenza A (H1N1) virus. A Phase 6 designation indicated that a global pandemic was occurring. The pandemic was declared officially over by the WHO on 10th August 2010. The HPA (UK) has issued guidelines, on swine flu treatment and management. Eating pork is not dangerous. It is spread from human to human. Also look at CDC and WHO guidelines and updates

Swine flu outbreak (2009-10)

• Swine influenza (also swine flu) refers to influenza caused by any strain of the influenza virus endemic in pigs (swine). Strains endemic in swine are called swine influenza virus (SIV)
• An influenza pandemic began in April 2009 with a (probably) new strain of H1N1 swine influenza virus (SIV), called SIV-0IV. H1N1 is a subtype of influenza A. It is also referred to as Mexican flu, swine-origin influenza, or 2009 H1N1 flu
• H1N1 is one of the strains of influenza A which causes seasonal outbreaks of flu in humans on a regular basis. H3N2 is another. But this latest version of H1N1 is different, from this years 'normal H1N1 strain' (which is included in the 08/09 flu vaccine): it contains genetic material that is typically found in strains of the virus that affect humans, swine, and possibly birds
• The infectious period is unknown. But for many viruses, 1 day before symptoms and 7 days after is often taken as this period

Introduction

• Swine flu is common in swine and rare in humans. People who work with swine, especially people with intense exposures, are at risk of catching swine influenza - if the swine carry a strain able to infect humans. However, these strains are rarely able to pass from swine to human; then human to human. Rarely, SIV mutates into a form able to pass easily from human to human
• The strain responsible for the 2009 swine flu outbreak in humans is believed to have undergone such a mutation
• The mortality is unknown
• It can disappear, then re-emerge in a more virulent form in the winter

Epidemiology/history

• 1918: The Spanish flu pandemic remains the most devastating outbreak of modern times. Caused by a different form of the H1N1 strain of influenza A (possibly avian), it is estimated that up to 40% of the world's population were infected; and more than 50 million people died - with young adults particularly badly affected
  1957: Asian flu killed two million people. Caused by a human form of the virus, H2N2, combining with a mutated strain found in wild ducks. The impact of the pandemic was minimised by rapid action by health authorities, who identified the virus, and made vaccine available speedily. The elderly were particularly vulnerable
  1968: An outbreak first detected in Hong Kong, and caused by a strain known as H3N2, killed up to one million people globally, with those over 65 most likely to die
• Direct transmission from pigs to humans is rare, with 12 cases in the US since 2005 - until the 2009 outbreak in Mexico
• The flu virus is perhaps the trickiest known to medical science; it constantly changes form to elude the protective antibodies that the body has developed in response to previous exposures to influenza or to influenza vaccines. Every two or three years the virus undergoes minor changes
• Then, at intervals of roughly once a decade, after the bulk of the world's population has developed some level of resistance to these minor changes, it undergoes a major shift that enables it to tear off on yet another pandemic sweep around the world, infecting hundreds of millions of people whose immune systems are largely ineffective. Even during the Spanish flu pandemic, the initial wave of the disease was relatively mild, while the second wave was highly lethal
• We were overdue an inflenza pandemic. There had not been one for about 40 years (ie 1968 outbreak). It is not clear why the pandemics seemed to be getting 'milder' (less deaths) over the 20th and 21st Centuries. Perhaps better public health medicine, and communications. Alternatively, it could be nothing to do with 'us'; and we simply are going through an evolutionary phase of reducing aggression of the organisms
• Swine flu virus might again mutate into something as deadly as the Spanish flu

Virulence/severity and mortality of 2009-10 outbreak

• In March and April 2009, over 1000 cases of suspected swine flu in humans were detected in Mexico and the southwestern United States. Although there were reports of "more than 100 dead from swine flu", the WHO received reports of only 7 confirmed deaths total and explicitly denied a large figure (April 29.4.09)
• The mortality of SIV-0IV is unknown. As most cases were mild, although very large numbers were affected, mortality was 'low' in relative terms. But, alternatively, if it had been a more lethal organism, with a high mortality but only affecting a few people - mortality would have been 'high'

Risk factors

• Contact with other humans in an epidemic area (Mexico, in 2009), or on their return
• Contact with other known, or suspected cases

Virology

• Of the three genera of human flu, two are endemic also in swine: Influenzavirus A (common) and Influenzavirus C (rare). Influenzavirus B has not been reported in swine
• Within Influenzavirus A and Influenzavirus C, the strains endemic to swine and humans are largely distinct

Other influenza A strains, and humans

• Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains
• It is thought that pigs can carry human influenza viruses, which can combine (ie exchange homologous genome sub-units by genetic reassortment) with another influenza A virus H5N1 (which caused 'bird flu'), passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift

Symptoms

• In humans the symptoms of swine flu are usually mild; similar to those of influenza and of viral illness in general. Symptoms include fever, cough, sore throat, body aches, headache, chills and fatigue
• In the 2009-10 outbreak, an increased percentage of patients reported diarrhoea and vomiting

Key questions

• "Have you just returned from an epidemic area, such as Mexico?"
• "Have you had contact with a known, or suspected case?"

Signs

• None specific

Size of an epidemic/pandemic

• Often difficult to estimate. The data from Mexico largely reflects hospital inpatients
• Large swathes of the countryside could have had many more unrecognised mild cases, where patients decided not to seek medical advice
• The data collection issue may have been less of a problem in the UK.

Investigation

Nose and throat swabs should be taken (according to local protocols) and then sent to a local HPU (Health Protection Unit), only if necessary

Blood

• FBC, ESR, CRP
• U+E, LFTs, Bone, Glucose
• BC

Other

• Nose and throat swabs should be taken (according to local protocols) and then sent to a local HPU (Health Protection Unit), if necessary
• Many countries, including the UK, rapidly moved on to the 'treatment phase' of the pandemic; ie, just treat, rather than investigate
• CXR (to exclude other diagnoses)

Specialist Investigation

• If nose or throat positive for influenza A, then patient should be considered a 'probable case'. Then send samples on to local HPU
• Then, if positive for 'H1' (or untypable), HPU will send on to Colindale for typing; and final confirmation of this 'H1N1 variant'

Differential Diagnosis

• Other forms influenza
• Other viral and bacterial illnesses

Treatment

Isolate patient ASAP (later cohorting may be necessary)

Treatment

Drugs

• PO OSELTAMIVIR (Tamiflu) 75 mg bd or PO ZANAMIVIR (Relenza) 10 mg bd, both 5 days. Treat if
• 1. CLINICAL condition warrants Rx: fever ≥38°C OR history of fever AND flu-like illness (two or more of the following symptoms: cough, sore throat, rhinorrhea, limb/joint pain, headache) OR other severe/life-threatening illness suggestive of an infectious process; AND
• 2. GEOGRAPHICAL association: onset of symptoms within seven days of visiting areas known to have incidents of probable human-to-human transmission of this outbreak of swine flu Mexico or United States; California, New York, Texas)
• Note: these are current guidelines, but frail elderly often do not mount a fever, or WC (CRP usually elevated). So, Rx, if you think probable case

Latest on Rx

• WHO have stated that the viruses obtained from human cases of swine flu in the United States were sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza) but resistant to amantadine and rimantadine. Tamiflu and Relenza also have a preventative effect against Influenzavirus A

• CDC has recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain (27.4.09)

Isolation and infection control etc

• Isolate supected patient, according to local policy
• Cohorting may necessary later, if more cases occur
• Wear PPE in suspected cases (personal protective equipment = high filtration mask, gown, gloves and eye protection)

Prescribing issues

• Treat, if necessary

Key management decision

• Treat/not (senior decision)
• Admit/not (senior decision)

Admit?

• Do not admit, unless essential

Bed plan

• Call seniors. Isolate
• See local policy - ie ?medical admission ward; then infectious disease ward, if have one

Referrals

• Microbiology
• Infection control
• Virology, if have one
• Local infectious disease unit, if necessary
• HPU if necessary

Vaccination

• A new vaccine is now available, but only given to certain at risk groups
• It is unclear how effective currently available flu vaccines would be at offering protection against the new strain, as it is genetically distinct from other flu strains
• The 2008/9 Northern Hemisphere influenza vaccination is active agaisnt 2 strains of influenza A, and one of B:
    A/Brisbane/59/2007 (H1N1)-like virus (but not this variant. How much cross-protection there will be is unknown)
    A/Brisbane/10/2007 (H3N2)-like virus
    B/Florida/4/2006-like virus
• A vaccine was used to protect humans from a version of swine flu in the US in 1976. However, it caused serious side effects, including an estimated 500 cases of Guillain-Barré syndrome

The Rest

Pigs can harbour influenza viruses adapted to humans and others adapted to birds, allowing the viruses to exchange genes and create a pandemic strain

Risk stratification

• Admit, on normal criteria for viral illness (severe sepsis, shock, complications etc)

Prognosis

• Probably good

2° Prevention + Health promotion

• Prevention of swine influenza has three components: prevention in swine, prevention of transmission to humans, and prevention of its spread among humans:
• Avoid epidemic areas. Face masks of limited benefit benefit, unless used correctly
• Hand-washing can help prevent viral infections; it is a surprisingly effective way to prevent ordinary influenza and the new swine flu virus. Influenza can spread in coughs or sneezes; the virus can also probably linger on tabletops, telephones and doorknobs - and other surfaces and be transferred via the fingers to the mouth, nose or eyes. AFTER HANDWASHING, a alcohol-based gel will work well to destroy viruses and bacteria
• Anyone with flu-like symptoms such as a sudden fever, cough or muscle aches should stay away from work or public transportation. Social distancing is another tactic. It means staying away from other people who might be infected and can include avoiding large gatherings; spreading out a little at work, or perhaps staying home and lying low if an infection is spreading in a community

Don't forget

• INVOLVE SENIORS EARLY, if suspect case
• Don't admit, unless essential
• Handwashing, alcohol gels etc important
• Isolate, according to local policy
• Health professionals handling patients: wear full PPE

Red flags

• Severe sepsis

References