U.S.A. — A study published in Cell Host & Microbe found that different stomach viruses tend to be more contagious when the virus particles cluster together.

The scientists conducted the study by analyzing stool samples from patients who had rotavirus or norovirus.

They found out that stomach virus such as norovirus and rotavirus cluster together to form "packs" of up to 40 viruses.

The virus clusters — called vesicles — are then covered in a protective membrane.

The virus inside the clusters are also quick to replicate inside the membrane to form more virus particles.

According to the study, the protective membrane protects the virus clusters from being noticed by the immune system.

As the vesicles pass through the immune system and into the intestine, it quickly separates and infects one single cell with multiple viruses.

In the study, scientists found that mice infected with clustered viruses became more ill compared to those that were infected with a single virus.

The researchers noted as there are currently no vaccine to treat the vesicles, treatments to target the clusters, instead of individual virus particles, would need to be developed.