East or West, cardiac arrest: air pollution effects similar worldwide. (Science Selections).

In many ways, Hong Kong and London are worlds apart. But researchers from the University of Hong Kong and St. George's Hospital Medical School in London found that air pollution patterns correlated with similar health effects in both, bolstering the argument that air pollution contributes to short-term health problems, no matter where it occurs [EHP 110:67-77]. The team's findings also add to the body of air pollution data by providing the first such information on a large subtropical city; other studies from around the world have been conducted almost entirely in temperate regions. However, the study still leaves questions unanswered, such as the specific mechanism by which these pollutants can cause harm. [See "Polluting Your Internal Environment," preceding page, for a theory about a possible mechanism.]

The research team reviewed data for daily emergency hospital admissions for the periods 1992-1994 in London and 1995-1997 in Hong Kong. Selected complaints included asthma in people aged 15-64, a range of respiratory diseases in people 65 and older, a range of cardiac diseases in people of all ages, and one subcategory of cardiac disease, ischemic heart disease, in people of all ages.

Hospital admissions for these complaints were compared with each city's concentrations of particulates 10 microns in diameter and smaller (P[M.sub.10]), nitrogen dioxide (N[O.sub.2]), sulfur dioxide (S[O.sub.2]), and ozone within three days before admission. The cities had roughly similar concentrations of each pollutant, except for P[M.sub.10], which was markedly higher in Hong Kong.

To evaluate other factors that can play a part in hospital admissions, the team analyzed variables such as temperature, humidity, day of the week, season, thunderstorm occurrence, and influenza outbreaks. They also analyzed the differences in the two cities in climate, demographics, hospital admission patterns, and other factors that might affect the diseases under consideration. For instance, only 3% of Hong Kong females who are 15 or older smoke, compared to 27% of those in London, while 27-28% of the males in each city smoke.

Despite many differences between the populations, a small but significant number of hospital admissions in each city were generally associated with changes in concentrations of the pollutants studied. This was particularly true for cardiac problems overall, which tended to increase with elevated concentrations of P[M.sub.10], N[O.sub.2], and S[O.sub.2] in each city. Ischemic heart disease followed the same general pattern, although admission numbers were statistically insignificant in Hong Kong. Respiratory problems tended to increase with elevated concentrations of P[M.sub.10], N[O.sub.2], S[O.sub.2], and ozone in each city in many circumstances. Other common threads appeared. For instance, respiratory illnesses occurred most frequently in each city's time of lowest humidity (the cool season in Hong Kong and the warm season in London).

The researchers acknowledge there were several idiosyncrasies in the data. Cardiac admissions tended to decline as ozone concentrations rose in London, while Hong Kong's ozone concentrations, although very similar to London's, had no significant link with cardiac admissions. In some cases, the effects of a pollutant decreased after a second pollutant was added to an analysis. And there was no significant link in either city between asthma and the pollutants studied. The researchers believe, however, that the similarities outweigh the differences, and that the study therefore "strengthens the argument for the causality of air pollution associations with hospital admissions."