Zara’s owner, Inditex, has reported underlying sales growth at its stores in every part of the world – with a little help from a white polka-dot midi dress which became the viral fashion hit of the summer.

The £39.99 Zara dress, which even had an Instagram Hot 4 the Spot, dedicated to sharing images of the dress being worn on the street, proved popular with women of all ages and was snapped up by customers ranging from the broadcaster Victoria Derbyshire to fashion bloggers, even becoming a uniform for hen parties.

Sales at the Spanish group’s established stores rose 5% in the six months to 31 July. Sales grew in stores across the world and online, as well as across all its store brands, which include Pull&Bear, Massimo Dutti and Bershka as well as Zara. The company said it expected growth to continue at a similar pace, with its early autumn/winter collections being “well received”.

The company said it had recently launched online stores in Bahrain, Oman and Kuwait and would do so in South Africa, Colombia and the Philippines this autumn.

Pre-tax profits rose nearly 9% to nearly €2bn in the most recent six months as total sales for the group rose to €12.8bn. However, the company’s share price fell nearly 4% on Wednesday as investors were disappointed that profit margins did not rise.

Inditex’s strong sales mark it out from many other struggling fashion retailers, including Topshop, New Look and Marks & Spencer.

Richard Chamberlain, a retail analyst at RBC, said Inditex had a proven track record of sales outperformance and the latest half year was no exception. “Even in its most mature market, Spain, Inditex achieved [underlying] sales growth of about 4%, ahead of the market’s growth of 3%, albeit its degree of outperformance has narrowed compared to previous years,” he said.