How can I make my javascript chat polling script be more efficient?

For some reason this check for new chat messages causes a larger amount of browser (and to some extent server) load than I would expect. Anyone see any ways that I can make it more efficient, to lessen the load?

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// Begin the cycle of refreshing the mini chat after the standard delay.
function startRefreshingMinichat(){
    var secs = 30; // Chat checking frequency.
    setTimeout(function (){
        checkForNewChats();
        startRefreshingMinichat(); // Loop the check for refresh.
    }, secs*1000);
}

// Check for the latest chat and update if it's different.
function checkForNewChats(){
    // Check whether the latest chat doesn't match the latest displayed chat.
    // NOTE THAT THIS CALLBACK DOES NOT TRIGGER IMMEDIATELY.
    $.getJSON('api.php?type=latest_chat_id&jsoncallback=?', function(data){
        var newChats = false;
        // Update global data stores if an update is needed.
        if(updateDataStore(data.latest_chat_id, 'chat_id', 'latestChatId', 'chat_id')){
            newChats = true;
        }
        if(newChats){ // there are new chats to show.
            refreshMinichat(null, 50); // loads new chat content.
        }
        // Since this callback isn't immediate, any feedback has to occur whenever the callback finishes.
 }); // End of getJSON function call.
}

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Check out CometD. It's a js long-polling system I've used with some success for simple chat systems integrated with jQuery. (Last time I looked, there were a few jQuery specific implemetations, but I never found one that was robust enough for me.)

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you can checkout this push engine so that you have not to poll for new data anymore. check it out, its really cool.