The attack rate of H1N1 in various berthing configurations on board an aircraft carrier

We compared attack rates for novel H1N1 influenza A (H1N1) among various groups aboard an aircraft carrier as influenced by characteristics of their living arrangements.

During an outbreak of H1N1 on board the USS George Washington (GW), group affiliation (department or squadron membership) data were obtained on all patients who were placed in respiratory isolation based on their diagnosis with presumptive H1N1. Because berthing spaces are assigned by department and various characteristics of each department's berthing spaces are known, analysis of attack rates in comparison to these characteristics was possible. Attack rates were compared with the square feet of living space per sailor, occupancy rate of the berthing areas, and size of the berthing areas. These results were further correlated with the mission of the various departments or squadrons.

The average attack rate was 3%, with the highest rates occurring in departments or squadrons whose mission required ongoing contact with civilian populations ashore. The attack rate among officers was 2.04 versus 3.19 among enlisted personnel; this difference was not significant (P = .21). The attack rate for women was 1.90 versus 3.09 for men, which was significant (P = .05). Although attack rates varied considerably based on organizational mission, no correlation was found between attack rate and square feet of living space per person or occupancy rate or size of berthing spaces.

The attack rate of the outbreak overall was limited to 3%. Smaller and more crowded berthing configurations did not contribute to higher attack rates, suggesting that transmission occurs most frequently elsewhere while engaged in other activities such as working, eating, or relaxing. Further studies are necessary to filter out potential correlations or variables not identified in this study, such as the difference between the number of men and women isolated.