Covid-19 clusters predominate in households

Crowding in poorly ventilated environments, where there is shouting and singing, increases risk of transmission

There is consistent evidence that clusters of SARS-CoV-2, the strain of the coronavirus which causes Covid-19, predominate in household settings, where they are associated with a higher secondary attack rate (SAR) compared with other settings such as healthcare, the Health Information and Quality Authority (HIQA) has stated.

HIQA made the observation in its latest advice to the National Public Health Emergency Team (NPHET) today (November 18), recommending that crowded indoor, and poorly ventilated environments, where there is shouting and singing, insufficient use of face coverings, and prolonged contact, present an increased risk of virus transmission.

While there is consistent evidence that the risk of transmission is substantially lower outdoors, the health regulator said that clusters in outdoor environments have been observed, particularly when there are large gatherings, limited physical distancing, dense congregation, and mixing among groups.

Commenting on the advice, Dr Máirín Ryan, Director of Health Technology Assessment and Deputy Chief Executive of HIQA, said the international evidence highlights that the main factors that contribute to spread of Covid-19 are indoor settings, crowds, and prolonged contact with others.

“Much can be done to mitigate risk in these settings, such as ensuring good ventilation and people following public health advice to use face coverings, keep physical distance and wash their hands frequently,” Dr Ryan added.

With HIQA also advising NPHET that the SAR for SARS-CoV-2 is high compared with other pandemic respiratory viruses, Dr Ryan said: “Our findings reinforce the importance of adherence to self-isolation guidance, despite the challenges it can pose, for those with Covid-19, those awaiting test results and those with symptoms suggestive of Covid-19.”

“This means following the Health Service Executive guidance on self-isolation including staying indoors, in a room with a window you can open, and completely avoiding contact with other people, including where possible other household members, for at least 10 days,” she added.

Other activities or settings where large numbers of clusters have been consistently observed, HIQA said, are nursing homes, hospitals, meat and food processing plants, large shared accommodation, sporting activities, bars, nightclubs and restaurants, gyms, offices, cruise ships, weddings, shopping malls, prisons, mines and religious settings.

“Many of these settings and activities have been associated with superspreading events and have seeded large numbers of cases,” the health watchdog added in its advice note, which is available on HIQA’s website,

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