Query Post not displaying correct category

I’m having trouble with the code below. It doesn’t seem to be displaying post from the specified category, instead it’s displaying all posts.

Thanks

<?php
		query_posts($query_string.'category=5&showposts=4');
		$counter=0;
		while (have_posts()) :
		$counter++;
		switch($counter) {

		case 1:
		case 2:
		the_post(); ?>
			<ul class="post">
				<li>
					<div class="news-post" id="news-<?php the_ID(); ?>">
					<div class="news-thumb news-main"><!-- Thumbnail Wrapper -->

						<h5 class="news-title"><a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title() ?></a></h5>

						<?php $image = get_post_meta($post->ID, 'thumbnail', true); ?>
						<a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><img src="<?php echo $image; ?>" alt="" /></a>

						<div class="post-date"><!-- Date -->
						<h2 class="date"><?php the_time('m/j') ?></h2>
						</div> <!-- /Date -->

					</div><!-- /Thumbnail Wrapper -->
					</div><!-- /Post ID -->
				</li>
			</ul>
        <?php
		break;
		case 3:
		$postslist = get_posts('category=7&showposts=1');
		foreach ($postslist as $adpost) {
			setup_postdata($adpost);
		?>
    	<li>
            <div class="ad-post" id="ad-<?php the_ID(); ?>">
            <div class="ad-thumb ad-main"><!-- Thumbnail Wrapper -->

                <h5 class="ad-title"><a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title() ?></a></h5>

                <?php $image = get_post_meta($post->ID, 'thumbnail', true); ?>
                <a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><img src="<?php echo $image; ?>" alt="" /></a>

            	<div class="post-date"><!-- Date -->
           		<h2 class="date">[Sponsored]</h2>
            	</div> <!-- /Date -->

            </div><!-- /Thumbnail Wrapper -->
            </div><!-- /Ad ID -->
		</li>
		<?php
		} // end foreach
		 // important: no break statement here

		case 4:
		the_post(); ?>
			<ul class="post">
				<li>
					<div class="news-post" id="news-<?php the_ID(); ?>">
					<div class="news-thumb news-main"><!-- Thumbnail Wrapper -->

						<h5 class="news-title"><a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title() ?></a></h5>

						<?php $image = get_post_meta($post->ID, 'thumbnail', true); ?>
						<a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><img src="<?php echo $image; ?>" alt="" /></a>

						<div class="post-date"><!-- Date -->
						<h2 class="date"><?php the_time('m/j') ?></h2>
						</div> <!-- /Date -->

					</div><!-- /Thumbnail Wrapper -->
					</div><!-- /Post ID -->
				</li>
			</ul>
        <?php
		break;

		} // end switch-case

		endwhile;

	?>