Goldie, I don't know the answer. What I do know is that I'm struggling with sinus congestion/cold symptoms since the end of December and I too was wondering if the CPAP has anything to do with it not going away. I've had such a bad cold that eventually lead to tonsillitis and a round of antibiotics, but I feel not a whole lot better. Congested every night and sneezing all day long. Still have to gargle with saltwater, as I can feel the tonsils swell up again (hard to swallow) when I stop. I have a pretty good hygiene routine for the CPAP, so really, I don't know what's going on, the doctor said a few weeks ago that I have a virus and to continue gargling with saltwater. This is my first winter on CPAP and I can't remember any other time a cold would linger on for so long.
As a microbiologist with 20 years experience in medical microbiology/infection control and 20 years experience in the sterile pharmaceutical production I strongly doubt you could get an infection from a CPAP. In general bacteria and fungi need moisture and a source of nutrients. There are bacteria that will grow in distilled water and on moist surfaces with no other nutrients but they are not pathogenic except to immune-suppressed people. The materials in hoses and masks contain no nutrients. Also you need to inhale them in fairly large numbers. The most likely source of nutrients is saliva and other fluids from your mouth and nose but they are confined to the mask and distal end of the hose because of the air flow and are easily controlled by regular washing with mild detergent.
I assume you wash your hose, mask, etc. with a mild detergent. The washing and drying will not remove all bacteria and fungi but will reduce the numbers to a level that is not a risk, even if there are pathogens present, which is unlikely. I assume your drying removes residual water. I connect my hose to my CPAP and run it for a couple of hours to dry the hose. Effective drying will also reduce the numbers of bacteria. Desiccation kills most of them, especially pathogens.
The filters do not protect you from infection. The air you breathe when not using the CPAP contains the same bacteria and fungi. The filters are to protect the machine from contamination with dust, etc which could damage it. They do protect you from the standpoint that to much dust from room air in the machine could provide nutrients for the growth of microorganisms from the room environment but it is very unlikely they would be pathogenic.
I am comfortable with washing my hose, mask, and humidifier once a week. I wash my cushions daily primarily to remove residual oils from my skin which interfere with sealing. I change my filter every couple of months or if it looks dirty. Filters actually become more effective at removing airborne particulates as they get dirty. The problem with a dirty filter is that it may reduce air flow to the point that the machine may be damaged, probably from overheating, because it needs to work harder to move the required amount of air.
It's unfortunate that you have a sinus infection. I know they can be miserable. It may be the antibiotics have not helped because it's caused by a virus. Mosquitobait is correct in saying that the antibiotic treatments may have set you up for a fungal infection by eliminating the harmless bacteria which are normally present. Steroids, however, although they may be an effective part of treatment, do not kill fungi. If you have a fungal infection (and that's a big if) you need treatments with an antifungal agent. I don't think, however, you need to be concerned about you CPAP as the source, especially given the maintenance schedule you follow.
Goldie, I wanted to add one final thing - there is a particularly nasty cold going around this year. MANY people get better for a week or two and then get a residual infection which can include a sinus infection. This could be related to your issue. Also, if you are diabetic, watch your blood sugar if you go on a steroid. It can really play havoc - you might even benefit from being on insulin during that time even if you don't normally take it.
Experience. The silicone seal feels a little tacky when clean and is less likely to slide. After I remove the mask in the morning I find it to be slippery. If I don't wash the cushions each day I have more leak problems. I also find it helps to wash my face well just before going to bed. I'm sure this may vary with individuals depending on how oily there skin gets especially around the nose and eyes.
Thanks for all of the suggestions. I will be calling the doctor in a half hour and explaining what is going on. He did mention that he wants me to see a ENT and I am hoping that I can get in soon, that way I can figure out what is going on. So sick of this!