Chembio Diagnostics Inc. on Wednesday announced the completion of its planned stock sale of 2.3 million shares, which raised $12.8 million for the Medford company.

The manufacturer of rapid tests for HIV and syphilis sold stock to the public for $6 per share. The sale began last week.

Chembio has struggled recently, posting losses for the past two years and projecting red ink for the quarter ended June 30. The company said last week that its cash balance at the end of June was $1.44 million, not including deferred revenue of $819,000.

Executives said Wednesday that proceeds from the stock sale, after expenses including the stock underwriter’s discount, will be used for test development, clinical trials, marketing and other activities.

Chembio shares on Wednesday closed down 13 cents, or nearly 2 percent, at $7.22 on the Nasdaq Stock Market. The shares have climbed $2.22, or about 44 percent, in the past 12 months.

Before the stock sale, Chembio had 9.7 million shares outstanding.

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Chembio has received a number of grants to develop point-of-care tests for Ebola, malaria, Zika and other diseases. Last week the company announced it had received approval to begin selling a Zika test in Europe and the Caribbean.

Last year Chembio lost $2.4 million, an increase over its 2014 loss of $1.1 million. Sales for 2015 fell to $24 million, a decrease of 12 percent from 2014.

About 155 people work at company facilities in Medford and Holbrook.