Broderick 2008.

Methods	Prospective, cohort study carried out in a military recruit training centre during the first 4 weeks of recruit training. Data were collected between February 2004 and March 2005 (duration of recruit training is not reported) It is not clear how the recruits were assigned to 'experimental' (closed) or control (open). Recruits were assigned to units on the basis of arrival order with no particular allocation scheme The study assessed if social distancing would reduce the incidence of febrile respiratory illness (FRI). Data were collected over 4 weeks for each new group of recruits Housing units (n = 196 units) were divided into closed units (n = 30) (experiment/intervention) or open units (n = 166) (control). For description of how the closed units were selected and geographical position in the training centre see notes Microbiological samples from physical structures (tables, surfaces, angles of surfaces, handles) of some units were done. However, it is not mentioned if these units were selected from among the closed or open units
Participants	Male military recruits (n = 13,114), distributed among 196 housing units (166 open units and 30 closed units) took part in the study. Unit size ranged from 44 to 88 recruits per unit. Reported denominators add up to 13488 recruits not 13114 (closed: 329/2099 versus open: 1586/11389). No exclusions were reported. Dimensions of the units are not described (space/subject or space/unit). The average number of subjects/unit in the closed units was not reported 10% of medical convalescent unit (MCU) subjects (762) and 6% of physical conditioning unit (PCU) subjects (395) were positive for adenovirus 4 by PCR
Interventions	To test the effect of social distancing: participants were either assigned (allocation process not clear) to closed or open units. The closed units did not introduce any new participants once their personnel had been assigned (socially‐distant); sick recruits were removed but if their symptoms did not require placement in the MCU, the recruits returned to their units. The open units accepted recovering subjects after being discharged from MCU and PCU To test an environmental aetiology: some of the units, which were vacant after 4 weeks of occupation, were swabbed. The MCU was also swabbed. The samples were tested by PCR and were cultured
Outcomes	Laboratory: (MicroTest M4 Transport; Remel) polymerase chain reaction (PCR) culture for Ad‐4 virus Not used to confirm FRI in all index cases. Adenovirus was the only microorganism tested for and isolated Effectiveness: cases of FRI were defined either by a body temperature of > 38°C and 1 respiratory symptom or by the presence of non‐febrile pneumonia Cases were reported as number of cases of FRI per 100 persons per week, averaged over the 4 weeks Safety: n/a
Notes	The institutional review board of the Naval Health Research Centre classified the protocol of this study as a non‐research public health endeavour. Given the flaws of the study design (the disparity between the number of closed and open units, testing 2 different ‘aetiological’ hypothesis using different methodologies and lack of information on how the units were selected), one gets the impression that this study was probably carried out at least retrospectively instead of being carried out as a prospective study as claimed by the authors. The authors conclude that social distancing did not reduce FRI and that environmental contamination rather than person to person transmission is the culprit in the spread of FRI. The method used for social distancing, however, did not exclude those that were little bit sick but did not require placement in the MCU. In other words, sick people were allowed to remain in the closed unit (? as well as in the open units); only apparently healthy recruits were allowed to rejoin the open units after being placed in the MCU and PCU The study put emphasis on the importance of environmental cleaning. In addition to that crowded areas increase the risk of transmission of viruses. In the study, however, it was not clear if open and closed units are similar or different as pathogen reservoir. Also, analysis of closed units according to the population size was not done and information about the location of the closed units (all over the centre or localised in certain (isolated) area) is lacking. Despite these clear limitations this pragmatic study's findings may be interpreted in a variety of different ways. Perhaps the most interesting interpretation is that environmental conditions are determinants of adenoviral infectivity but not entry and exit from a community. In other words virological and presumably bacterial agents persist in the environment, they are not “brought” in and do not “arrive” and do not directly and invariably cause one‐on‐one disease. This hypothesis challenges the current simplistic interpretation of the postulates of Henle‐Koch (one agent = one disease and suggests that the presence of microorganism may only be one of the many variables which determine infectious disease. This interpretation is comforted by the relatively small number of isolates found in studies of ILI causes (so called pie studies) The corresponding author provided the following additional information: each week a new cohort of about 500 recruits arrives at the camp, all of whom arrive by Wednesday. On Thursday the recruits are assigned to 6 platoons (each platoon housed in its own large room ‐ called "housing units" in the article). Each cohort's 6 housing units are numbered from 1 to 6, with no particular distinction between them. Each house is given approximately the same number of recruits. The placement of the recruits into the housing units is based somewhat on the order of their arrival to the camp, but otherwise there are no criteria for placement, although relatives and friends are allowed to be in the same platoon. The recruits at MCRD San Diego tend to be from west of the Mississippi. There is no particular order of arrival at the camp from different regions. The number of the closed housing unit assigned in each cohort varied. In the majority of cases it was 1 or 2 Each building contains 4 wings of 3 floors each. From the sky, the buildings form an H shape. The line in the middle of the H connects the sides of the H, and on each side the half above the middle line is one wing and below the middle line is the other wing. If you go on maps.google.com and type in 'san diego ca mcrd' and zoom in on C you can see how big the buildings are. The housing units for each cohort typically occupy 2 wings one building, but occasionally one housing unit will be in a different building. E.g. if there are 6 housing units in a cohort, the cohort will occupy 3 floors of wing A and 3 floors of wing C. The map gives you an idea of the geography of horizontal distance between each wing, and each floor is about 10 feet high. Although the housing units are relatively close to each other, the platoons do not typically interact with each other. They are large permanent buildings each consisting of 12 large rooms and a hallway
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	N/A
Allocation concealment (selection bias)	Unclear risk	N/A
Blinding (performance bias and detection bias) All outcomes	Unclear risk	N/A
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	N/A
Selective reporting (reporting bias)	Unclear risk	N/A