Gingivostomatitis can develop due to certain viruses or bacteria. These include: Herpes simplex virus type 1 (HSV-1). The most common cause of gingivostomatitis, HSV-1 is the same virus that causes cold sores. Streptococcus. This bacteria commonly causes strep throat or blood infections, but it can also result in gingivostomatitis. Actinomyces. This bacteria naturally occurs in the mouth, but it can lead to gingivostomatitis if it enters the oral tissues. This may occur following oral surgery or trauma to the mouth. Coxsackieviruses. A common group of viruses, coxsackieviruses usually spread due to unwashed hands or other surfaces contaminated with feces (poop). Coxsackieviruses also commonly cause hand, foot and mouth disease.