Issaquah, Wash. — Costco Wholesale Corp. has reported a 12.5% increase in quarterly net sales in its fiscal fourth quarter, which ended Aug. 30. Costco’s sales jumped to $52.9 billion from $46.4 billion last year. Costco also experienced a 91% jump in quarterly e-commerce sales, resulting in a 50% increase over the previous year. The company’s net income for the fourth quarter was $1.4 billion, compared with $1.1 billion last year, even though this year’s fourth quarter was negatively impacted by $281 million in costs related to COVID-19 — such …