When’s the last time you picked your nose? If you’re an adult, it was very probably earlier today – the average adult picks their nose around 4 times per day (eew). And that’s picking – touching is much more frequent: on average, we touch our eyes, mouth, nose, or chin a staggering 20 times per hour (with some estimates even higher). We’ve known for a while that nasal decolonisation is a vital component in reducing the risk of staphylococcal infection. But using mupirocin as the nasal decolonisation agent has important limitations in terms of spectrum of microbiological efficacy, compliance, and antibiotic resistance. I’ve recently come across a newer technology for nasal decolonisation: nasal photodisinfection. It’s been around for ages, but hasn’t really been adopted widely. This blog provides an overview of three studies that suggest nasal photodisinfection may have a role in reducing the risk of SSI, and in preventing and treating SARS-CoV-2 infection.

Nasal photodisinfection

The only commercially available nasal photodisinfection system currently on the market uses light to activate methylene blue combined with a low concentration chlorhexidine as a biocide. This provides broad spectrum antimicrobial efficacy, including activity against bacteria (both Gram-positive and Gram-negative), fungi, and viruses. The treatment takes between 5-10 minutes in total, and is well-tolerated. The general idea is that you do a single photodisinfection treatment vs. a course of mupirocin ointment (or possibly intranasal octenidine).

Preventing SSI

Perhaps the most obvious application for nasal photodisinfection is to prevent SSI in surgical categories where staphylococci predominate as the causative pathogen. To massively over-simplify things (see more detail in Table 4a of this UKHSA report), Gram-positive bacteria and especially Staphylococcus aureus predominate in orthopaedic and spinal surgery, Gram-negatives in bowel surgery, and it’s even-stevens in cardio-thoracic procedures. Around 10 years ago, a hospital in Vancouver, Canada implemented nasal photodisinfection combined with chlorhexidine skin decolonisation prior to “clean elective” cardiac, orthopaedic, spinal, vascular, thoracic, and neurosurgical procedures. A total of 6090 patients met the inclusion criteria, and 5691 received photodisinfection. Microbiological sampling immediately before and after photodisinfeciton treatment showed that a semi-quantitative reduction in S. aureus growth was detected in around 85% of patients, with around half of patients with S. aureus prior to photodisinfection remaining culture-negative for at least 48 hours after treatment. Only 6% of cases were eligible for photodisinfection but not treated; of these, most were due to operational challenges (e.g. patients arriving early or going straight to theatre), and only 5% were due to patients declining. Mild and short-term pharyngeal irritation was noted in 0.1% of patients; no serious adverse events were recorded.

SSI rates during the year-long evaluation were compared with historical data over the previous four years. Overall, the SSI rate was 1.6% in the patients who were treated compared with 2.7% in the historical control group. Perhaps unsurprisingly, the lion’s share of this reduction was in orthopaedic and spinal specialities. To account for confounding, the team also analysed patients who were treated with those who were not during the evaluation period, and identified a similar picture in terms of SSI reduction.   

The outcomes in this study are impressive, recording substantial reductions in SSI risk in a number of important surgical categories. It’s not possible to disentangle the relative impact of implementing pre-operative chlorhexidine bathing and nasal photodisinfeciton, since both were implemented simultaneously. However, the study does provide evidence that SSI risk can be reduced without the need to turn to mupirocin, which suffers from a narrow spectrum of efficacy, compliance issues, and the threat of resistance.

Current NICE SSI prevention guidelines in the UK recommend the use of nasal mupirocin combined with chlorhexidine skin decolonisation before ‘procedures in which Staphylococcus aureus is a likely cause of a surgical site infection’ (with the exact procedures to be determined locally). The guidelines also recommend active surveillance for mupirocin resistance. US guideline recommendations, for example the recently updated SHEA Compendium, are broader and less prescriptive in terms of approach, recommending decolonization with an ‘antistaphylococcal agent’ for all orthopaedic and cardiothoracic procedures, and additionally for procedures at high risk of staphylococcal SSI. Whilst the SHEA Compendium recommendations centre around mupirocin as the antistaphyloccal agent, there is passing reference to other options including photodisinfection. 

So, where does this leave us for photodisinfection and the prevention of SSIs? There’s good evidence that nasal decontamination using mupirocin is an effective way to reduce the risk of staphylococcal SSI and whilst the evidence base isn’t great, there is compelling evidence that nasal photodisinfection will do this job at least as well. However, the carrot is that nasal photodisinfection offers the potential to go beyond preventing staphylococcal SSIs and prevent SSIs caused by other organisms for which the nose is a reservoir (remember how many times you touch your nose in an hour…!).

SARS-CoV-2

Another area where the use of nasal photodisinfection has been evaluated is in the prevention and treatment of SARS-CoV-2 infection. A placebo-controlled randomised trial assigned 38 patients to placebo and 37 to photodisinfection for 3 days of treatment early in mildly symptomatic COVID-19. Patients assigned to photodisinfection had significantly reduced infectivity at day 3 post treatment, and increased chances of being PCR-negative by day 7. Also, photodisinfection has a measurable impact in reducing the degree to which immunity waned in the 20 days after the infection. This study provides some evidence that a therapeutic application of photodisinfection could play a role in treating respiratory infectious diseases.

An interesting study evaluated the impact of nasal photodisinfection in the prevention of SARS-CoV-2 infection in an industrial workplace setting. The study was undertaken in a food processing plant in Canada, where the 1500 employees were offered weekly photodisinfeciton therapy from July 2020. Importantly, photodisinfection was implemented along with a range of other measures, including improved hand and environmental hygiene, physical distancing, and testing. The rate of laboratory-confirmed COVID-19 in the factory workers was significantly lower than in the regional population. Since so many interventions were put in place concurrently, it’s difficult to interpret the meaning of the study in the context of nasal photodisinfection, aside from feasibility of large-scale implementation.

Next steps/future

Key areas for further research include:

• What is the impact of nasal photodisinfection on the microbiome?
• Could nasal photodisinfection be a more effective way to decolonise patients colonised with MRSA in health and care settings?
• What is the comparative effectiveness of nasal photodisinfection compared with other approaches for nasal decolonisation (such as mupirocin, povidone iodine, and octenisan)?
• How does cost effectiveness look for nasal photodisinfection in various applications?
• And, finally, is there a way to apply a photodisinfection approach to decolonisation at other body sites, or the treatment or prevention of a wider spectrum of infectious diseases (I’m thinking of a “photodisinfection chamber”!)

Nasal photodisinfection is a really interesting approach, and as we begin to come towards the end of some key antibiotics, it’s a really good time to explore the use of biocides in the prevention and treatment of infectious diseases. Whilst the nose is the key niche for staphylococci, it’s a microbial zoo in there, and given the frequency with which we touch our noses, you can see how effective nasal decolonisation has potential to do more than reduce staphylococcal infection.