An article in this week's 9/11 special issue of The Lancet written by Dr Hannah Jordan, Dr Steven Stellman, and colleagues at the World Trade Center Health Registry, New York City Department of Health and Mental Hygiene, NY, USA assesses the all-cause mortality in 9/11 NYC World Trade Center (WTC) survivors. So far, the study revealed that exposed rescue workers and civilians have lower death rates than a comparable sample of the New York City population.
Researchers extracted data from the New York City vital records and the National Death Index of WTC Health Registry participants who resided in New York City and died between 2003 and 2009. The data was categorized into rescue and recovery workers (RRWs) including volunteers, or non-rescue and non-recovery (NRNRs) participants, including lower Manhattan residents, area workers, school staff and students, and commuters and passers-by on 9/11.
Researchers used their calculations of New York City's standardized mortality ratio (SMR) from 2000 to 2009 as comparison reference group and calculated the relative mortality risk within the cohort for participants with high and medium exposure compared to those who had low exposure.
After identifying 156 deaths in 13,337 RRWs and 634 deaths in 28,593 NRNRs from the records, researchers determined that all deaths combined were 43% less likely to have died from any cause than the New York City general population (SMR 0.57) after adjusting for age, sex, race, and calendar year. RRWs were 55% less likely to have died from any cause (SMR 0.45) compared with the city's general population, while NRNRs were 39% less likely to die (SMR 0.61). The researchers did not find any increased SMRs for respiratory-, heart diseases or blood cancers.
NRNRs with intermediate and high levels of WTC-related exposure showed a significantly high link to mortality, i.e. 22% and 56 % respectively compared with low exposure. NRNRs with high exposure levels had a double-increased risk to die from heart disease-related mortality compared to those with low exposure.
Higher exposure was not linked to higher all-cause mortality in RRWs.
The authors commented:
"Because most illnesses that are established or possible sequelae of WTC-related exposures have long latency or long median survival periods, the absence of a relation between reported dust-cloud exposure by itself and mortality risk in our study is not surprising."
According to the researchers there are two reasons for lower mortality in WTC-exposed individuals; the first being the commonly recognized 'worker cohort effect' in that with the majority of the exposed consisting of employees, these usually have a healthier constitution than the general population.
Secondly, health study volunteers, such as the WTC Health Registry are also usually also of better health than the general population. Because the 'healthy worker' and 'healthy volunteer' effects are expected to disappear over time, excess deaths among WTC Health Registry enrolees that occur in the future will be possible to be identified through the registry's on-going analyses.
The most common conditions associated with 9/11-exposure have been respiratory and mental illnesses. According to the researchers, WTC-exposed individuals also have a risk of suffering a premature death due to newly diagnosed and existing respiratory diseases, as well as complications of mental disorders, including substance abuse and other risk taking behaviors.
Cardiovascular disease (CVD) has been linked to pollutant exposure and psychological stress in other settings. For this reason increased CVD mortality rates might have resulted from 9/11-related exposures.
The researchers also evaluated the risk of cancer due to concerns about potential exposures to carcinogens in the WTC dust cloud; however, studies can only commence from this point of time, as the time span since the WTC disaster has been too short to start any complex scientific processes of determining whether or not cancer may be associated with WTC exposure.
Most cancers have a large variety of risk factors and can take decades to develop with the exception of some types of blood cancer, which can develop a few years after exposure.
In a concluding statement the authors write:
"Among World Trade Center Health Registry participants residing in New York City, overall death rates in 2003-09 were not higher than expected when compared to the general New York City population.
However, within the cohort, non-rescue and non-recovery participants with high levels of WTC-related exposure had an increased risk of all-cause mortality and heart-disease-related mortality compared with those with low exposure. Continued monitoring of all-cause mortality and disease-specific mortality will be needed."
Dr James M. Feeney from the Saint Francis Hospital and Medical Center Hartford, CT, USA, and Dr Marc K. Wallack of the Metropolitan Hospital Center in New York City, USA say in a linked comment:
"Outside of psychiatric research, few data on the long-term sequelae of any terrorist event exist, but researchers caring for the WTC victims and responders are systematically rectifying that lack of reliable information. The study by Jordan and colleagues replaces supposition and assertion founded on anecdote with cold, hard, incontrovertible, well-presented data. Most of the focus on disaster management is on preparation, critical mortality, and response, and that is why this article is so important. As a society, the more data we have about the events, plans, opportunities responses, motivations, modus operandi, and especially the aftermath, the more devices we have to take the terror out of terrorism."
Written by Petra Rattue