Health experts warned that smokers could carry deadly bacteria which could pass on to their children.

Professor Robert Booy in his researh found that people who smoke are also prime candidates for carrying the potentially deadly meningococcus bacteria in the back of their throats.

The bug can be passed to children through normal family cuddles and kisses, he says, and one in 10 children who go on to develop the rare meningococcal disease will die from it.

Passive smoking isn't the only smoking risk to children, said Prof Booy, who is director of research at the National Centre for Immunisation and Research at Sydney's The Children's Hospital at Westmead.

Smokers carry more germs like meningococcus, so normal family cuddles and kisses can pass on dangerous germs, even if smokers only smoke outside.

Prof Booy pointed to recent University of Sydney research, which showed almost 92 per cent of NSW residents aged over 16 report they live in a house that is smoke-free.

He said this showed how many parents who smoked went outside to indulge their habit and this would reduce a child's risk of passive smoking-related middle ear infection and asthma, or even Sudden Infant Death Syndrome.

But smoking outside did not reduce the increased threat posed by meningococcus, Prof Booy said, adding that cases of its resulting disease usually spiked during winter.

This is another good reason for smokers to quit, not just smoke outside, he said.

Although its rare, meningococcal disease can be serious and up to 10 per cent of patients can die.

With the beginning of winter now here, we are now entering the peak season for meningococcal disease.

The symptoms of meningococcal disease may include a sudden onset of fever, severe headache, weakness, drowsiness, confusion or coma, sore legs or sore joints, nausea and vomiting, a dislike of bright lights, a stiff neck and a rash of red-purple spots.

Prof Booy said with early detection and treatment, the majority of children with meningococcal disease would make a full recovery.