Weather and the risk of sudden infant death syndrome: the eVect of wind

Study objective—To examine and identify relations between sudden infant death syndrome (SIDS) and wind, particularly the föhn wind, in Christchurch, New Zealand. Design—A retrospective epidemiological study combining details of regional hourly meteorological variables and reported SIDS cases. Setting—Christchurch, New Zealand, between 1968 and 1997 inclusively. Participants—All 646 infants reported as dying from SIDS within the greater Christchurch region. Main results—Analysis of 1968–1989 data revealed nine wind variables significantly related to SIDS. When compared with corresponding variables calculated over the 1990–1997 period, only the northerly wind on the day of death and the southerly wind three days before a SIDS death had estimated associations with similar eVect size and sign. However, both these variables had confidence intervals that included unity. Conclusions—No evidence was found to suspect that föhn winds influenced SIDS occurrence. The relations identified between SIDS incidence and wind, after controlling for the eVects of temperature and trend, were tenuous and relatively small. More data are necessary to substantiate whether northerly winds on the day of death or southerly winds occurring three days before a death are truly associated with SIDS. It seems that wind has little, if any eVect on SIDS incidence in Christchurch. (J Epidemiol Community Health 2000;54:333–339) Sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in many developed countries, including New Zealand. Despite extensive international research, much remains unknown about the exact causes or mechanisms that lead to such deaths. One of the consistent epidemiological features of SIDS found throughout the world is that of seasonality, with SIDS occurring more frequently in colder months. Various day and lagged day ambient temperature eVects have also been associated with SIDS. The significance of these temperature measures has prompted speculation that other localised meteorological patterns may also aVect SIDS incidence. Historically, one of the more important climatic factors associated with ill health, other than temperature, has been that of wind, particularly hot, dry and turbulent wind. Internationally, this type of wind has many nomenclatures, including: the föhn (or foehn) wind in Switzerland and Germany; the Santa Ana or witches wind in the USA; the Sirocco in south eastern Europe; the Chinook in Canada; the Zonda in the Andes; and, the Sharav in Israel. Föhn winds have been associated with increased irritability, headaches and heart problems. 13 15 16 In Bermuda, such winds have also been related to worsening asthma. However, not all studies have demonstrated deleterious associations between wind and health. Few studies have specifically related meteorological patterns, other than ambient temperature, to SIDS. Among those that have, one identified an association between visibility and SIDS, but found no statistical evidence for associations between wind speed, precipitation, cloud, or pollution levels. Another study noted that SIDS incidence increased on drier and windier days, but this finding was not explicitly related to föhn wind occurrence. The reason why föhn winds should aVect health is uncertain, although various postulates have been promulgated in the literature. 23 24 One theory suggests that these winds increase the proportion of positive ions in the atmosphere, which, in turn, adversely aVects our endocrine, vegetative and autonomous nerve systems. 25 26 Increased SIDS incidence could thus occur directly, through increased positive ion exposure, or indirectly, through altered infant care practices in response to föhn wind conditions (such as caregiver irritability or headaches). Wind is undoubtably an important environmental factor. The question that arises is how much influence does climatic wind have on infants’ SIDS risk? The purpose of this study was to examine and identify relations between wind and SIDS on data collected over 30 years from 1968 to 1997 in Christchurch, New Zealand. Methods The objective is to examine and identify relations between SIDS and environmental wind once trend components and ambient temperature measures have been accounted for in the statistical model. CHRISTCHURCH METEOROLOGICAL DATA The New Zealand Meteorological Service supplied hourly recorded meteorological data, for the years 1968–1997, collected from J Epidemiol Community Health 2000;54:333–339 333 Community Paediatric Unit, Canterbury Health, Christchurch, New Zealand P M Macey P J Schluter R P K Ford