You are a PA in a GP practice and you are seeing a 2-year-old boy with his mother. She has reported that her son has been generally unwell over the last couple of days and has now developed a sudden onset of a seal-like barking cough and shortness of breath. She is also worried about this strange noise he is making when he is breathing in. On examination you note that he has a seal-like barking cough with stridor and sternal recession at rest with no agitation or lethargy. What category do the patient’s symptoms come under?