Technical definition of Infection according to medical experts:
It is the transfer of disease from the sick to the healthy through different mediums such as breathing, touching and blood.

The most probable opinion from the definitions of infection is the transfer of microorganisms that course sickness, by close examination; it will overpower the minimum nausea dose, whereby it will penetrate the anti-bodies and reached it inner tissues, or the inner organs in the body such as the blood, fluid, and will affect the reaction of the body; dominate and destroying it and this is the final reaction which is known as inflammation.

The legal ruling on diseases infection from the Sunnah perspective

There have several reported legacies from the Prophet Muhammad pbuh concerning infection of diseases, some of it confirms infection while others negate it, and these legacies are as follows:

The Hadiths that confirm Infection of diseases:

Abu Hurairah reported the prophet pbuh to have said: ((Do not bring the sick person together with the healthy) narrated by al-Bukhari.

Ibn Abass (R.A) reported the prophet pbuh to have said: ((Do not keep on looking at the lepers) narrated by Ibn Majah.

The Hadiths that negate infection of diseases:

From Anas bn Malik (R.A) who reported the prophet pbuh to have said: ((There is neither transfer of infection nor from flow of birds and being optimistic for good really impressed me,)) narrated by al-Bukhari.

From Jabir bn Abdullah (R.A) who reported the prophet pbuh to have said: ((There is neither transfer of infection nor from flow of birds nor devilish notations)) narrated by Muslim.

The most probable view about Infection of diseases:

The Imam Anawawiyy said : the means of combination between hadith that negate infection means the negation of the belief by the people of ignorant who assume and belief that sickness and calamity can transfer by its nature without the permission and power of Allah, but the hadith that says: “ the sick people should not be mixed with the healthy ones” is an advise to be careful of mixing with people that has medical issues which might transfer with the permission and mighty of Allah, so the negation in the first hadith with the nature of infection which does not negate the occurrence of infection in that situation with the mighty and  permission of Allah which He gave advise in the second to be careful and cautious about whatever difficulty that happened to man is with the permission  will and mighty of Allah.

However, The most probable from the hadith of infection is the combination between the two, because the hadith of negation means negation of what is usually assumed in the period of ignorant by presuming and believing that sickness and pessimism occurred by itself and not from permission of Allah, and the established hadith indicates that it is not permissible to assume and belief as such but it is allowed to ascribe reasons and symptoms to the occurrence of calamity, by distancing the victims with the fair of transfer of infection to the healthy one by the permission of Allah. In order that devil will not whisper into him from what afflicted him because of the infection.

This is the correct view in accordance with the opinion of most scholars which most preferable.