Update on swine flu virus in US


Cases of a new variant virus of swine origin, influenza A (H3N2) virus associated with contact with pigs have been reported in the United States this summer. At the current time, the threat of infection to the European (including Irish) population is assessed as very low. Monitoring and preparedness are essential as this assessment may change in the future.

United States
Human cases of influenza A(H3N2)v have been reported in the United States since July 2011. From July 12 to September 6, 2012, a total of 296 infections with influenza A (H3N2) variant (H3N2v) viruses have been reported from ten US states. This is an increase of 8 over last week’s report. Cumulative totals by state since July 15 are: Hawaii [1], Illinois [4], Indiana [138], Maryland [12], Michigan [5], Minnesota [2], Ohio [102], Pennsylvania [11], West Virginia [3], and Wisconsin [18]. Sixteen H3N2v-associated hospitalizations and one H3N2v-associated death have been reported. The vast majority of cases have occurred after prolonged exposure to pigs, though instances of likely human-to-human transmission have been identified. At this time no ongoing human-to-human transmission has been identified. Public health and agriculture officials in the US are investigating the extent of disease among humans and pigs, and additional cases are likely to be identified as the investigation continues.

The majority of the persons infected had direct contact with pigs or attended an agricultural fair where pigs were present. However, a small number of people have caught the virus from other people (human-to-human transmission). The Centers for Disease Control and Prevention (CDC) in Atlanta expects that cases will continue to be detected including some due to human-to-human transmission.

The majority of infections occurred in children and teens and studies have shown that younger children are more likely to catch the virus. Most of the cases resulted in mild symptoms similar to seasonal influenza, such as fever, cough, sore throat, runny nose, tiredness, and headache. Therefore it is hard to tell the difference between the symptoms of influenza A(H3N2)v infections and those of seasonal influenza.

The current seasonal influenza vaccines are unlikely to provide protection to this swine flu virus. On a precautionary basis a vaccine strain has been developed in the US for use in production of influenza A(H3N2)v vaccines, if needed. Clinical trials to evaluate the effectiveness and safety of this vaccine are planned in the next few months.

As a result of enhanced surveillance activities for H3N2v, three infections with influenza A (H1N2) variant (H1N2v) virus have been detected in Minnesota in patients who became ill after contact with swine. One patient was hospitalized, but all have recovered from their illness. Confirmatory testing at CDC identified H1N2v with the matrix gene from the 2009 H1N1 influenza virus in specimens collected from all three patients. Although cases of H1N2v have been detected previously, the current cases mark the first reports of H1N2v with the matrix gene from the 2009 H1N1 virus.

In EU/EEA Member States, the influenza A(H3N2)v viruses have not been identified in pigs to
date, and no human cases have been reported. Therefore, there is currently no known risk of becoming infected with H3N2v viruses in Europe (EU/EEA countries).

The European Centre for Disease Prevention and Control (ECDC) published a risk assessment Swine-origin triple reassortant influenza A(H3N2) variant viruses in North America on August 17th which is available here.

It is possible that these variant virus infections will appear in Europe, particularly if there is more human-to-human transmission or travellers visiting US agricultural exhibitions, which could lead to imported cases.

Advice for Irish travelling to the US
Those travelling to the affected states in the US (Hawaii, Illinois, Indiana, Maryland, Michigan, Minnesota, Ohio, Pennsylvania, West Virginia and Wisconsin) who have contact with pigs on farms or visit agricultural exhibitions may be at risk of being infected. Persons who are at higher risk of influenza complications including those aged 65 years or older, young children and those with chronic medical conditions should avoid exposure to pigs and to persons who are ill following exposure to pigs while in the US. If exposure to pigs in the US cannot be avoided, persons at higher risk of influenza complications should consider wearing appropriate personal protective equipment.

In the event of returning Irish travellers developing influenza-like symptoms after exposure to pigs in the US (within 5-7 days of onset of illness), clinicians should consider and sample for the influenza A(H3N2)v viruses. The National Virus Reference Laboratory (NVRL) can undertake viral investigations to detect the virus if required. Clinical management of influenza A(H3N2)v as recommended by CDC is similar to the management of seasonal influenza A or B virus infections. The current Irish Guidance on the infection control measures and the use of anitivirals should be applied-available at http://www.hpsc.ie/hpsc/A-Z/Respiratory/Influenza/SeasonalInfluenza/.

Other Links


HPSC: Information on influenza here