160 Clinical Presentation

Chapter 8: Clinical Presentation

Christian Hoffmann and Bernd Sebastian Kamps

Uncomplicated Human Influenza

After a short incubation period of 1–2(–4) days, onset of the disease is usually abrupt with typical systemic symptoms: high fever and chills, severe malaise, extreme fatigue and weakness, headache or myalgia, as well as respiratory tract signs such as non-productive cough, sore throat, and rhinitis (CDC 2005) (Tables 1 and 2). Among children, otitis media, nausea, and vomiting are also common (Peltola 2003). In rare cases, the initial presentation may be atypical (febrile seizures, RyanPoirier 1995; bacterial sepsis, Dagan 1984).

Table 1. Typical symptoms of uncomplicated influenza

Abrupt onset

Systemic: feverishness, headaches, myalgias (extremities, long muscles of the back; eye muscles; in children: calf muscles), malaise, prostration

Respiratory: dry cough, nasal discharge – may be absent in elderly people who may present with lassitude and confusion instead

Hoarseness, dry or sore throat often appear as systemic symptoms diminish Croup (only in children)

Table 2: Frequency of baseline symptoms*

Symptom	(%)
Fever ≥ 37.8°C	68
Feverishness**	90
Cough	93
Nasal congestion	91
Weakness	94
Loss of appetite	92
Sore throat	84
Headache	91
Myalgia	94

*In 2,470 patients with laboratory-confirmed influenza (adapted from Monto 2000) **Defined as the patient’s subjective feeling that they had a fever or chill

The severity of clinical presentation varies from afebrile respiratory symptoms mimicking the common cold to severe prostration without major respiratory signs and symptoms, especially in the elderly. The severity of symptoms is related to the severity of the fever.

Fever and systemic symptoms typically last 3 days, occasionally up to 4–8 days, and gradually diminish; however, cough and malaise may persist for more than