9.7. Influenza

Standard Operating Procedure for Surveillance of Influenza

Effective Date: [Date]

Version: 1.0

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INFLUENZA

Overview

Influenza is an acute systemic febrile respiratory disease of world-wide distribution. It affects all age groups and can more severely affect certain age groups and persons with underlying conditions. The importance of the virus lies in its epidemic and pandemic potential, which has led to international surveillance of the disease coordinated by the WHO. The 2009 influenza pandemic was caused by serotype A H1N1 (H1N1pdm09) which now circulates as a seasonal serotype along with influenza A H3N2.

Due to increased inter-island travel for business and tourism, influenza can spread quickly between the islands. The most prevalent strains in the region have been influenza A (H1N1) and H3N2). Due to a high burden of chronic disease in the region influenza can potentially have a severe impact on the population. Additionally, the region is prone to increasing numbers of disasters such as hurricanes and earthquakes. Influenza like illness infection rates commonly increase in the conditions after disasters which may leave large numbers of people living in confined spaces or without enough shelter. 

There are 3 types of influenza virus that cause illness in humans, A, B and C. Types A and B are associated with epidemics and type C with sporadic disease. Isolated strains can be typed (A, B) and subtyped (A / H3N2, A / H5N2). Influenza A viruses, which affect both humans and animals, contain 2 major antigens, haemagglutinin (H) and neuraminidase (N). These antigens are subject to frequent major and minor changes, resulting in new sub-types which are responsible for epidemics or pandemics, depending on their ability to spread.

Due to rapid antigenic variation, influenza vaccine formulation is changed each year to reflect the prevailing strains detected by a laboratory-based surveillance system. Trivalent vaccine is manufactured containing 2 influenza A and one B strain and is offered annually to persons in high-risk groups.

Mode of Transmission

Influenza is spread from person to person by respiratory droplets that are produced when an infected person coughs, sneezes and speaks. Transmission can also occur indirectly by contact with infectious secretions on objects (fomites). The incubation period is 2-3 days. Persons are infectious up to 1 day before and seven days after the onset of symptoms.

Clinical Presentation

The infection is characterized by fever, chills, headache, myalgia, malaise, mild sore throat, coryza and cough. Individuals may experience disease ranging from mild respiratory illness to fatal viral pneumonia.

It affects all age groups, however, the elderly, and those compromised by chronic pulmonary, cardiac or metabolic disease are more susceptible to severe disease and death.

Surveillance Procedures: 

Step 1: Case Detection and Reporting – Healthcare Providers / Laboratory Personnel 

Immediately report all suspected cases. Reports should be shared with laboratory personnel for confirmation. 

Case Definitions

Key messages (WHO, 2013)

• Influenza infection causes a clinical syndrome not easily distinguished from other respiratory infections.
• The case definitions for Acute Respiratory Illness (ARI), influenza like illness (ILI), and severe acute respiratory infection (SARI) are not necessarily intended to capture all cases but to describe trends over time.
• Using one common case definition globally will allow national health authorities to interpret their data in an international context.

Suspected case

1. ARI case definition 
   1. An acute respiratory infection – (having at least one of the following: shortness of breath; cough, sore throat, coryza) with:
      1. reported fever of ≥ 38°C; 
      2. and cough;
      3. with onset within the last 10 days
2. ILI case definition
   1. An acute respiratory infection with:
      1. measured fever of ≥ 38 C°;
      2. and cough;
      3. with onset within the last 10 days.
3. SARI case definition
   1. An acute respiratory infection with:
      1. history of fever or measured fever of ≥ 38 C°;
      2. and cough;
      3. with onset within the last 10 days;
      4. and requires hospitalization.

Confirmed case

• Laboratory confirmed case: An ARI, ILI, or SARI case with positive RT-PCR for influenza.
• Epidemiologically confirmed case: an ARI, ILI, or SARI case linked to a laboratory confirmed case in an epidemic situation.

Step 2. Laboratory Confirmation

Samples should be taken to the labs to be tested (collection and transport details below)

Laboratory Diagnosis

For the purposes of surveillance, laboratory confirmation can be by any of the following, however RT-PCR is the most common diagnostic test:

• Conventional or real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to identify influenza viral RNA.
• Viral antigen detection by immunofluorescence or enzyme immunoassay methods (including commercially available bedside tests).
• Viral culture with a second identification step to identify influenza viruses (immunofluorescence, haemagglutination–inhibition, or RT-PCR).
• Four-fold rise in antibody titre in paired acute and convalescent sera.

Specimen Collection and Transport

• Oropharyngeal and nasopharyngeal swabs (Dacron)
  • These are collected within the first 5 days of onset of illness, placed in viral transport medium, and shipped to the laboratory within 24 hours on wet ice. If this is not possible, specimens should be stored at –70°C and shipped on dry ice to the laboratory.
• Nasopharyngeal washings
  • These are collected within the first 5 days of onset into a sterile vial and transported immediately to the laboratory on wet ice.
• Blood samples
  • Acute and convalescent samples may be drawn from a number of suspected cases, the former within 3 days of onset and the latter 14 days later. The serum is separated by centrifugation and sent in sterile tubes to the laboratory for serological testing.

Note:  Specimens a and b are preferred for Influenza diagnosis.

Step 3: Treatment and Prevention and Control

• The current formulation of influenza vaccine should be administered before the season, or prior to an anticipated outbreak. Target groups are individuals at risk mentioned below. Healthcare workers and those in essential community services should also be protected by vaccination.
• The drugs currently recommended for the treatment of influenza A and B are the neuraminidase inhibitors (e.g. Oseltamivir, Zanamivir and peramivir). Each country should maintain a stock of these antivirals for the treatment of influenza especially ahead of the flu season.
• Appropriate antibiotics should be used if secondary bacterial pneumonia is suspected.

Step 4. Reporting 

Reports of all confirmed cases should be shared with the Epidemiology Unit 

Step 5: Data Management (Epi Unit) 

• Data should be cleaned and analysed 
• Preparation of a report should be done on the evolution of the epidemiological  situation of the disease 
• Dissemination of a weekly situation report 

If an outbreak occurs: 

Outbreak Investigation and control

• The detection of a new subtype of influenza should be reported to the WHO via the regional IHR focal point.
• Detection of levels of influenza above seasonal baselines should trigger the activation of the country’s influenza plan and the necessary control measures.
• Once an outbreak is confirmed, efforts should be made to obtain information on travel, exposure to animals, occupation, vaccination, comorbidities, etc.
• Follow up all contacts with possible exposure and educate them on the need to monitor for development of symptoms and how to seek health care should symptoms develop.
• Quarantine individuals with likely exposure for the standard incubation period to watch for development of symptoms. Testing should be done according to international protocols for the current strain.
• The public should be educated about appropriate hand hygiene and about exercising proper cough and sneeze etiquette. They should also be advised to avoid unnecessary contact persons who are sick.
• Crowding of large numbers of people in enclosed places should be avoided.
• During an influenza epidemic, attempts should be made to prevent severe disease in persons at high risk (the elderly; cardiac patients; those with chronic health conditions such as bronchitis, emphysema, asthma; those with renal disease or diabetes; persons with immunosuppression; children under 5 years; and pregnant women). 
• In addition to using standard Infection Prevention and Control measures at health care facilities the following steps should be taken:
  • Health care workers should routinely wear PPE consisting of a surgical mask, protective eyewear and disposable gloves if they are undertaking an examination that may lead to coughing in an individual with an acute respiratory illness (e.g., collecting nose/throat swabs)
  • Infectious patients should wear a surgical mask when not in isolation.
  • Erect signage at the entrance to general practice, emergency departments and outpatient settings requesting that patients with ILI should inform reception staff immediately on arrival, should don a surgical mask, and perform hand hygiene.
  • Highlight the importance of hand hygiene and respiratory hygiene/cough etiquette amongst patients and staff. 
  • Residential or long-term care facilities and hospital wards will need to take additional precautions to limit exposures to infected persons and to stop the spread of the virus.

Notes:

Animal Health Surveillance 

Several animal species may act as a source of flu viruses. Flu viruses are known to cause disease and are transmitted among animals, such as domestic and wild birds, pigs, horses, dogs and cats. The 2009 H1N1 pandemic and others were caused by flu viruses in animals that acquired the ability to infect and spread easily in humans; because of this public health agencies such as the CDC and infectious disease experts around the world monitor flu viruses that circulate in animals.

CARPHA’s Medical Microbiology Laboratory provides confirmation of influenza infection in humans using PCR. Nasopharyngeal or oropharyngeal swabs, aspirate or washes should be collected within 1 to 7 days from the onset of symptoms and sent to the laboratory for testing according to the instructions above.

The following events should be monitored in the veterinary sector:

• Reports of respiratory syndromes in farm animals identified by veterinarians.
• Unexplained deaths of farm animals such as chickens and wild birds.
• Domestic animals with respiratory syndromes identified at veterinary clinics.
• History of contact with domesticated birds or visit to live bird markets in patients with ILI or SARI.

Environmental Health

Influenza like illnesses normally shows seasonal variation throughout the year. The flu season generally coincides with the dryer and cooler months of the year (November to March). There is also a suggested relation between the levels of Sahara dust in the atmosphere and respiratory disease in the Caribbean. 

Increases in worker absenteeism can be a sign of increased morbidity due to influenza when outbreaks have occurred. Surveillance of reasons for medical leave can supply valuable information on flu related morbidity among workers. When analysed by sector, workers at increased risk may be identified.

The following parameters should be monitored:

• Seasonal variation in rainfall, humidity, temperature and corelate with the trends in influenza like illness, acute respiratory infection and severe acute respiratory infections.
• Air quality, including the seasonal variation in Sahara dust and its relation to respiratory diseases identified in humans.
• Worker absenteeism and medical leave claims during flu season.

Traveller’s Health

Typical outbreaks of influenza in the Northern hemisphere begin in early winter. As such the flu season also coincides with the winter tourist season in the Caribbean which generally extends from November to March. 

Surveillance at ports of entry is vital for the detection and control of outbreaks of respiratory diseases, paying special attention to the following:

• Ensure that all arriving ships have completely and accurately completed the maritime declaration of health, paying attention to the threshold of level of infection before pratique is granted.
• Ensure that the health declaration is accurately completed by the captain of all arriving aircraft before port health clearance is given.
• Syndromic surveillance at tourist accommodations should be maintained to allow for early detection of priority diseases and outbreaks.