Enid Blyton 
The Mystery of the Strange Bundle [EPUB ebook] 

“Of all the miserable holidays these just about beat the lot!” said Pip to Bets. “Why you had to start us off on this awful ‘flu’ I can’t imagine!”
Bets looked hurt. “Well, I couldn’t help it, ” she said. “Someone gave it to me before I gave it to you others. It was jolly bad luck that it happened at Christmas.”
Pip blew his nose violently. He was sitting up in bed, feeling decidedly better but very bad-tempered.