RIO DE JANEIRO/BRASILIA (Reuters) - The coronavirus outbreak is landing in Brazil as the hot summer days in the southern hemisphere draw to a close and winter approaches, potentially worsening the spread of the virus, medical experts told Reuters.
Little is known about how changes in seasonal weather affect the new coronavirus, which has sparked a snowballing global crisis. Nonetheless, six infectious disease experts in Brazil said that past outbreaks in the country, including the 2009 H1N1 swine flu pandemic, point to colder temperatures exacerbating contagion.
Brazil is already the hardest hit country in Latin America, with 621 confirmed cases by Thursday - more than doubling in two days.
Although much of Brazil is tropical, monthly temperatures in parts of the south and southeast can average 5-6 degrees Celsius (41°F-43°F) in June and July. Temperatures start falling in April, when flu infections tend to rise, experts said.
"There's never a good moment for the coronavirus to arrive... but this is not a good moment," said Maria da Gloria Teixeira, an epidemiologist at the Federal University of Bahia.
The concerns are echoed in other southern hemisphere countries. Australia has had a similar number of confirmed cases as Brazil, but authorities have said they expect that to increase rapidly as the winter arrives.
That could also apply to other South American countries like Argentina and Chile, which are less populous than Brazil but have colder weather.
Infectious disease experts say they cannot be sure if the coronavirus is seasonal, because it has not been around long enough to gather enough evidence. However, with respiratory diseases like colds and flu scientists think cold air causes nasal and airway irritation that makes people more susceptible to infection.
In Brazil, disease experts pointed to concerns for the south.
Aside from being Brazil's coldest region, it also has an older population, according to the 2010 census. In Rio Grande do Sul, Brazil's southernmost state, 20% of people were 60 or more.
In Italy, which on Thursday overtook China as the country with the most coronavirus deaths, around 23% of the population is 65 or over. Seniors are the most vulnerable to COVID-19, the respiratory disease caused by the virus.
A study by the University of Sao Paulo's Institute of Tropical Medicine on the 2009 swine flu outbreak confirmed the highest incidence of infections was in Brazil's three coldest and southernmost states. A 2006 study found that pneumonia and influenza deaths peak in Brazil's southern states during winter.
"We can surmise that the coronavirus will conform to the same framework," said Expedito Luna, an Institute of Tropical Medicine researcher.
Thursday was Brazil's last day of summer. The government has forecast the outbreak will peak in April and May. But as the seasons change, those estimates could go out the window.
José Cássio de Moraes, an epidemiologist at the Santa Casa Medical Science University of Sao Paulo, said winter could worsen the epidemic because people are more likely to crowd indoors. A seasonal spike in colds may also weaken immune systems and lead to more coughing, which spreads the virus.
Tania Vergara, the president of the Infectology Society of Rio de Janeiro State, said heat likely weakened the ability of the virus to survive on places like doorknobs or in the air.
"This is an advantage for us right now when it's hot," she said. "It won't be an advantage going forward."
The less affluent north of Brazil generally stays hot year-round. But it, too, faces risks, the Federal University of Bahia's Teixeira said.
"Social problems among poorer populations are a variable that always worsen epidemics," she said.
(Reporting by Gabriel Stargardter and Jake Spring, Editing by Rosalba O'Brien)
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