What further testing should be done for a 6-month-old infant diagnosed with respiratory infection and apnea when bacterial cultures are negative?

When a 6-month-old infant presents with a respiratory infection and apnea, with bacterial cultures yielding negative results, further testing for respiratory syncytial virus (RSV) is indicated. RSV is a common viral pathogen that causes respiratory infections, particularly in infants and young children. It is known for its ability to lead to severe bronchiolitis and pneumonia, which can manifest as wheezing and apnea, especially in this age group.

In the context of respiratory symptoms, testing for RSV is crucial because it is one of the most prevalent viruses causing lower respiratory tract infections in infants. Early identification of RSV can affect management and treatment decisions. For instance, in severe cases, supportive care, such as oxygen therapy or hospitalization, may be warranted.

The other options, such as rotavirus and Norwalk virus, are primarily associated with gastrointestinal infections and would not be appropriate tests in cases specifically linked to respiratory symptoms. While HIV can lead to a range of infections including respiratory issues in infants due to immune suppression, it is less likely to be the first consideration in a case of acute respiratory infection presenting with apnea, especially in an otherwise healthy infant. Therefore, focusing on RSV testing aligns well with the clinical presentation and age of the patient.