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Infection > Influenza > Flashcards

Influenza Flashcards

1
Q

What kind of virus is the influenzae virus and what family is it from?

A

RNA virus with an 8 segment genome

Orthomyxoviridae family

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2
Q

What are the main groups of influenza virus, and who/what do they affect?

A

A, B and C

A infects mammals and birds
B and C infect only human

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3
Q

What influenza viruses are most commonly seen?

A

A and B - A is global and infects humans, mammals and birds so is seen widely, B tends to be in smaller outbreaks

C tends to cause milder infections so may not be recognised as flu

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4
Q

What are the surface proteins of the influenza virus and what are their functions?

A

Haemagglutinin - facilitates viral attachment and entry into host cell

Neuraminidase - enables new virion to be released from host cell

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5
Q

How many different antigens of the influenza virus surface proteins are there?

A

18 different haemagglutinin antigens (only H1-3 affect humans)
11 different neuraminase antigens

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6
Q

What is the antigenic drift?

A

Mechanism of genetic variation within the virus

Occurs continually over time, with small ongoing point mutations in the genes encoding for the antibody binding site

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7
Q

How does antigenic drift affect the outcome of influenza virus infection?

A

Changes the antigenic properties so eventually the immune system will not combat the virus as well, which will cause worse than normal epidemics and vaccine mismatch

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8
Q

What is the antigenic shift?

A

Abrupt major changes in the virus, process by which two or more different strains of the virus combine to form a new subtype resulting in new H/N combinations

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9
Q

What does the antigenic shift enable?

A

A flu strain to jump from one animal species to another

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10
Q

What does the antigenic shift result in?

A

Reassortment of the virus’s gene segments
New antigenic properties meaning the population at risk is unprotected
Can lead to pandemics

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11
Q

When does seasonal influenza occur?

A

In the winter months

December to February in the Northern hemisphere and June to August in the southern hemisphere

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12
Q

What were the major 20th century flu pandemics?

A

1918-1919 Spanish Flu
1957-1958 Asian Flu
1968-1969 Hong Kong Flu
2009-2010 Swine flu

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13
Q

What was the timeframe in which the pandemic of Swine Flu (2009-2010) affected different countries?

A

First case recognised on March 17th in Mexico
Onset of first cases recognised on March 28th in Mexico
By May 18th, 40 countries were affected
By June 19th, 81 countries were affected

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14
Q

What percentage of the population are affected by seasonal flu?

A

10-15%

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15
Q

When does pandemic flu occur and who does it affect?

A

Occurs sporadically

Affects 25% + of the population

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16
Q

What is the difference in severity of illness between seasonal and pandemic flu?

A

Seasonal flu is usually unpleasant but not life threatening, pandemic flu is more serious and occurs with more complications

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17
Q

What are the requirements for pandemic flu?

A

Human pathogenicity
New virus resulting in susceptible population
Efficient person-person transmission

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18
Q

Features of Avian Flu

A

Spread through direct contact with infected birds (dead or alive)
Few strains which affect humans
High case fatality rate

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19
Q

What are the modes of transmission of influenza?

A

Airborne - person to person via large droplets (> 5 microns)
Contact - direct person to person or indirect person to fomite to person

20
Q

When does virus shedding occur?

A

Usually in the first 4 days of illness, can range from 1-7 days
Longer in children and the immunocompromised

21
Q

What is the influenza survival on non-porous and porous surfaces?

A

24-48 hours on non-porous surfaces

8-12 hours on porous surfaces

22
Q

Investigation of flu

A 
Viral nose and throat swabs 
CXR 
Blood culture 
Pulse oximetry 
Respiratory rate 
U&Es 
Creatinine 
FBC 
CRP
23
Q

Clinical features of flu infection

A

Incubation period of 2-4 days
Abrupt fever of up to 41 degrees which lasts 3 days
Plus 2 or more of; cough, sore throat, rhinorrhoea, myalgia, headache, malaise

Less common symptoms are nausea, vomiting and diarrhoea

24
Q

Groups at high risk of contracting flu infection

A

Chronic respiratory disease, particularly those with continuous oral steroid use
Chronic heart, renal, liver or neurological disease
Diabetes mellitis
Immunosuppression
Morbid obesity
Pregnancy

25
Q

At what stage of pregnancy are women at the highest risk of flu infection?

A

Third trimester

26
Q

Common respiratory complications of flu infection

A

Acute bronchitis
Secondary bacterial pneumonia
Community MRSA (uncommon in UK/Europe)

27
Q

Uncommon complications of flu

A

Primary viral pneumonia

Myocarditis
Pericarditis

Transverse myelitis
Guillain-Barre
Myositis and myoglobinuria

28
Q

Features of Encephalitis Lethargic, which occurred as a flu complication in 1918

A 
Fever, headache, lethargy, sleep reversal 
External ophthalmoplegia 
25% mortality 
Post-encephalitic Parkinsonism 
Serology positive for flu A
29
Q

When should patients with flu symptoms be given an urgent CXR?

A

When flu symptoms and fever are present for more than 4 days

30
Q

What score is used to assess the severity of a flu infection?

How is it scored?

A

CURB 65

C- confusion 
U - urea > 7mmol/l
R - respiratory rate > 30mm
B - Blood pressure diastolic < 60 or systolic < 90 
65 - > 65 years old
31
Q

How does the CURB65 score correlate to the risk of death within the next 30 days?

A 
0 - 0.6% 
1 - 3.2% 
2 - 13% 
3 - 17% 
4 - 41.5%
5 - 57%
32
Q

When should antivirals be used in the treatment of influenza?

A

ASAP, within 48 hours of onset

Should always be given in complicated illness, regardless of how long after the onset of illness it is

33
Q

Antivirals used in influenza treatment

A

Oseltamivir

Zanamivir

34
Q

Dose of Oseltamivir for influenza

A

In over 13 years old;

75mg every 12 hours for 5 days

35
Q

Possible side effects of oseltamivir

A

Nausea
Vomiting
Abdominal pain
Diarrhoea

Less common - headache, hallucinations, insomnia, rash

36
Q

Dose of Zanamivir for influenza

A

Available only as dry powder inhaler

Over 12 years old;
10mg inhaled daily for up to 10 days

37
Q

Possible side effects of Zanamivir

A

Rare

Occasionally bronchospasm

38
Q

Other antivirals not used in the UK for influenza

A

Peramivir - only licensed in USA
Favipiravir - licensed in Japan
Armantidine and Rimantidine - no longer used due to resistance

39
Q

What is the current guidance for flu treatment with antivirals in pregnancy?

A

Benefit should outweigh risk

Current guidance is oral oseltamivir

40
Q

When are patients with influenza considered non-infectious?

A

Immunocompetent adults

  • 24 hours after last flu symptoms
  • or when anti viral therapy is completed

Immunocompromised patients and young children need to be considered on a case-by-case basis with regards to when they are non-infectious

41
Q

Protection for healthcare staff against influenza

A

Surgical face mask, apron, gloves
Wash hands after examination
Use a face-fit FFP3 respirator mask when seeing patients who are receiving a nebuliser with aerosolised virus

42
Q

How is the flu vaccination prepared?

A

Seasonal flu vaccine is prepared each year using viruses considered most likely to be circulating in the forthcoming winter
Grown in the allantoic cavity of chick embryos
Chemically inactivated and purified

43
Q

In what patients is the flu vaccine contraindicated?

A

Those with an egg allergy

44
Q

How is the flu vaccine administered?

A

As a single 0.5ml intramuscular injection

45
Q

Why are healthcare workers immunised against flu?

A

To protect themselves and their families
To reduce the risk to at-risk patients
To reduce absences from work during influenza surge

Infection (14 decks)

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