Total mortgages purchased and securities issued by Freddie Mac reached $27.7 billion in August, up 33% from the previous month and the highest increase since September 2010. Purchases and issuance rose to the highest level since February, according to the government-sponsored enterprise’s monthly summary report released Friday. The increase in August offset the drop measured the previous month. The increased activity reflects a boost in home sales in the same month, according to the National Association of Realtors. Freddie’s guarantee book of business stayed essentially flat at $1.69 trillion in August after dropping below $1.7 trillion in July. It remains at the lowest level measured since October 2007. The single-family serious delinquency rate of 90 days or more dropped to 3.49% in August. In July, it increased for the first time in 10 months. The August rate is the lowest since September 2009, and the rate hasn’t been below 3% since July 2009. Freddie continued to trim its mortgage-related investment portfolio in August, dropping it to $680 billion, down $3 billion from the prior month. Under the conservatorship agreements established in September 2008, the Treasury Department capped this portfolio at $900 billion at the end of 2009 and scheduled it to be wound down by 10% each year, reaching $250 billion by 2018. Write to Jon Prior. Follow him on Twitter @JonAPrior.