Super-spreaders
residential apartment complex. A man who had contracted SARS-CoV at a hospital while he was being treated for a separate condition stayed at Amoy Gardens for a few days. After one month, over 300 residents of the apartment complex tested positive for SARS-CoV. Investigations suggested that diarrhoea of the super-spreader that had been flushed formed aerosols which passed into neighbouring apartment blocks through the plumbing system. 5 The densely populated nature of the apartment complex likely facilitated further human-to-human transmission. In these examples, characteristics defining the super-spreaders are related to the varying behavioural and environmental factors of the host leading to increased social exposure to either the host or a contaminated area. A study by Temime et al. (2009) used a computer model to look at how noncompliance with hospital procedures, such as hand hygiene, among different healthcare worker (HCW) roles affects superspreading potential of hospital-acquired infections by HCWs of the bacteria erythromycin- resistant Staphylococcus aureus (ERSA) and methicillin-resistant S. aureus (MRSA) in an intensive care unit (ICU). Temime et al. (2009) found that the impact of noncompliance was strongest when the peripatetic HCWs (who engage in contact with many patients around the hospital, for example staff heads who pay a visit to every patient in the ICU) was noncompliant, and that peripatetic HCWs may have increased super-spreading potential compared to HCWs of other roles. Instances of super- spreading by peripatetic HCWs have indeed been documented, for example in 1983, where outbreaks of ERSA in two separate hospitals were traced to a single nurse who worked at both hospitals. 6 It remains true that social exposure play an important role as a characteristic of super-spreaders in a hospital or healthcare setting. It is also possible that super-spreaders are a result of biological factors. In Hong Kong during the 2003 SARS-CoV outbreak, one super- spreader was observed to have a ‘runny nose’, which was unusual for patients of SARS, 7 and it has been suggested that patients with different symptoms for unknown biological reasons may likely be super-spreaders, although for SARS specifically this has not been proven. However, there have been many documented cases where super-spreading of one disease is linked to co-infection – simultaneous infection of different pathogens in an individual. Eichenwald et al. (1960) showed that a group of infants infected with Staphylococcus aureus became much more contagious when also infected with a respiratory virus, shedding much higher loads of Staphylococcus aureus , describing the infants as ‘cloud babies’. The previously mentioned super -spreading nurse from 1983 was also found to be infected with a respiratory virus. 8 Similarly, a study by Bassetti et al. (2005), measuring the airborne dispersal of Staphylococcus aureus in adult carriers inside a sealed room, found a significant increase in airborne dispersal of Staphylococcus aureus after the volunteers were inoculatedwith a rhinovirus. The viruses in the examples all caused an upper respiratory tract infection (URI); Sherertz (1996) suggests that swelling of nasal turbinates as a result of an URI forces high-speed airflow and generates aerosols containing the pathogen that suspend in the air, allowing for greater ease of transmission and super-spreading potential. There is positive correlation between this specific coinfection of respiratory viruses and Staphylococcus aureus , and the super-spreading of S. aureus in such an infected individual. It can be suggested that biological factors such as co-infection, possibly as a result of decreased immunity, play a role in making certain hosts become super-spreaders.
5 Normile 2013. 6 Belani et al. 1986. 7 Wong et al. 2004. 8 See note 6.
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