In this report, we documented a substantial increase in the rate of pneumonia-related hospital admissions and deaths in Kesennuma among adults of all age groups soon after the Tohoku earthquake and tsunami. The clinical and microbiological characteristics of the post-disaster patients were similar to those of the pre-disaster patients. The vast majority of the victims were older people. Because this disaster affected a notably aging population with the highest baseline pneumonia incidence rate, the disaster caused a drastic increase in the number of admissions and placed a heavy burden on local hospitals.
Although the causal mechanism was not fully established, our findings suggested that multiple factors have contributed to this outbreak. The largest increase in the pneumonia burden was observed in nursing home residents, the majority of which were older people with physical and mental limitations and needed assistance with daily activities. A sudden change in their living environment after the disaster, such as a lack of appropriate nutrition, the loss of regular medicines and a shortage of caregivers, must have worsened their conditions.16
It should be noted that many caregivers were also victims who lost their families, friends and homes. This may have been reflected by the fact that the highest mortality rate among patients from nursing homes occurred in the early post-disaster period (results not shown). A high incidence was also observed in the residents of evacuation shelters. Crowding is a risk factor for S pneumoniae
and H influenzae
and we found that these pathogens, particularly H influenzae
, were isolated more frequently in patients from evacuation shelters.
The increased incidence observed in all residential places suggests that other factors which were shared by all survivors have also played an important role. First, hypothermia is known to increase the risk of subsequent infections, including pneumonia.19
On 11 March, it was snowing in northern Miyagi. All survivors were suddenly left without running water, gas, electricity or oil in freezing weather (−3 to −5°C at night; see online supplementary appendix figure 3
). The majority of the evacuation shelters were not sufficiently equipped with heating and blankets immediately after the disaster. Second, people experience stress reactions after the disaster. Psychological stress weakens the immune system and may increase the risk of respiratory infections.21
Third, the medical supply systems have drastically changed. Soon after the disaster, more than a hundred relief teams arrived in Kesennuma and initiated care for survivors; this change may have increased the chance of identifying patients with pneumonia.
The abovementioned reasons also explain the decline in pneumonia cases after May; the temperature increase, improvements in living conditions (water, gas and electricity had been fully restored by the end of May), recovery of medical supplies, and the decline in the number of evacuees reduced the risks of pneumonia. However, in our study, it was impossible to know what factors have truly contributed to this outbreak.
Pneumonia outbreaks after natural disasters have never been documented in the past. In 2005, Nishikiori and colleagues conducted a cross-sectional survey (n=3533 individuals) in Sri Lanka after the Indian Ocean tsunami,23
and no deaths were reported between one week and two and a half months after the tsunami. The different findings in Sri Lanka may be explained by the difference in population structures. If we projected our age group-specific estimates onto a population in Sri Lanka, where the proportions of people aged ≥65 years and ≥80 years in 2004 were 7% and <0.5%, respectively, the overall impact on pneumonia admission and mortality would decrease by almost 80%. Therefore, it is plausible that the impact of disasters on pneumonia incidence was overlooked in developing countries with relatively young populations.
A comparable event may have been observed in Japan after the Hanshin-Awaji earthquake that occurred in Hyogo Prefecture (where 15% of the population were aged ≥65 years) in January 1995. Among 1948 patients admitted for illness during the first 15 days after the earthquake, 418 (21%) had pneumonia. Their average age was 66 years,24
although population-based impact estimates were unavailable. In contrast, no pneumonia outbreak was documented after Hurricane Katrina, which occurred during the summer.25
Freezing temperatures may be a critical factor in pneumonia outbreaks after a disaster.
In our study, eight cases of near-drowning-related pneumonia were identified. Pneumonia associated with the aspiration of tsunami water drew global attention after a series of melioidosis cases among the Indian Ocean tsunami survivors was reported.8–10
This condition has been sometimes referred to as ‘tsunami lung’, which is defined as pneumonia caused by the aspiration of tsunami water containing soil, oil and sewage.27
However, there is no evidence that this condition is distinct from seawater drownings unrelated to tsunami disasters. Furthermore, the clinical characteristics of victims of the Indian Ocean tsunami may not be comparable to those of patients in settings where Burkholderia pseudomallei
is not endemic, as in our case. Natural disasters do not cause new diseases that are not endemic to the affected area.29–31
The term ‘tsunami lung’ must be used with caution to avoid media sensationalism.
The limitations of our study arise from the nature of hospital-based data collection. In Japan, 70% of the medical costs for people aged <70 years and 80–90% of the medical costs for people aged ≥70 years are covered by insurance,32
and all medical fees for the disaster-affected people were waived after 11 March.33
The cost was not a barrier to hospitalisation throughout the study period. Non-pneumonia diseases, such as heart failure, might have been misdiagnosed as pneumonia during the post-disaster period especially among older patients. However, the cases in this study were confirmed by experts using a standardised case definition, and the microbiological confirmation rate was similar between the pre-disaster and post-disaster period. Thus, the impact of misclassification and potential changes in admission criteria on our incidence estimates must be minimal. However, due to the limited microbiological data, the aetiology of our cases was not fully established.
Pneumonia and pneumonia-related deaths among older people have been overlooked in emergency preparedness and humanitarian responses, most likely because both are common events in this population. The key findings of our study are: disaster-affected people, especially those exposed to stressful living conditions, are at high risk of developing pneumonia and pneumonia-related death during the emergency phase of a disaster; and the pneumonia burden becomes substantial in areas with an aging population. This situation may arise in low-income and middle-income countries, as their populations are rapidly aging.34
In addition to using the PPV23 or pneumococcal conjugate vaccine for disaster-affected populations, the provision of optimal living conditions, medical check-ups and oral hygiene care must be a priority for older people after natural disasters.35